// #pragma GCC target("avx2") // #pragma GCC optimize("O3") // #pragma GCC optimize("unroll-loops") #include using namespace std; namespace templates { // type using ll = long long; using ull = unsigned long long; template using pq = priority_queue; template using qp = priority_queue, greater>; #define vec(T, A, ...) vector A(__VA_ARGS__); #define vvec(T, A, h, ...) vector> A(h, vector(__VA_ARGS__)); #define vvvec(T, A, h1, h2, ...) vector>> A(h1, vector>(h2, vector(__VA_ARGS__))); // for loop #define fori1(a) for (ll _ = 0; _ < (a); _++) #define fori2(i, a) for (ll i = 0; i < (a); i++) #define fori3(i, a, b) for (ll i = (a); i < (b); i++) #define fori4(i, a, b, c) for (ll i = (a); ((c) > 0 || i > (b)) && ((c) < 0 || i < (b)); i += (c)) #define overload4(a, b, c, d, e, ...) e #define fori(...) overload4(__VA_ARGS__, fori4, fori3, fori2, fori1)(__VA_ARGS__) // declare and input // clang-format off #define INT(...) int __VA_ARGS__; inp(__VA_ARGS__); #define LL(...) ll __VA_ARGS__; inp(__VA_ARGS__); #define STRING(...) string __VA_ARGS__; inp(__VA_ARGS__); #define CHAR(...) char __VA_ARGS__; inp(__VA_ARGS__); #define DOUBLE(...) double __VA_ARGS__; STRING(str___); __VA_ARGS__ = stod(str___); #define VEC(T, A, n) vector A(n); inp(A); #define VVEC(T, A, n, m) vector> A(n, vector(m)); inp(A); // clang-format on // const value const ll MOD1 = 1000000007; const ll MOD9 = 998244353; const double PI = acos(-1); // other macro #ifndef RIN__LOCAL #define endl "\n" #endif #define spa ' ' #define len(A) ll(A.size()) #define all(A) begin(A), end(A) // function vector stoc(string &S) { int n = S.size(); vector ret(n); for (int i = 0; i < n; i++) ret[i] = S[i]; return ret; } string ctos(vector &S) { int n = S.size(); string ret = ""; for (int i = 0; i < n; i++) ret += S[i]; return ret; } template auto min(const T &a) { return *min_element(all(a)); } template auto max(const T &a) { return *max_element(all(a)); } template auto clamp(T &a, const S &l, const S &r) { return (a > r ? r : a < l ? l : a); } template inline bool chmax(T &a, const S &b) { return (a < b ? a = b, 1 : 0); } template inline bool chmin(T &a, const S &b) { return (a > b ? a = b, 1 : 0); } template inline bool chclamp(T &a, const S &l, const S &r) { auto b = clamp(a, l, r); return (a != b ? a = b, 1 : 0); } template T sum(vector &A) { T tot = 0; for (auto a : A) tot += a; return tot; } template vector compression(vector X) { sort(all(X)); X.erase(unique(all(X)), X.end()); return X; } // input and output namespace io { // vector template istream &operator>>(istream &is, vector &A) { for (auto &a : A) is >> a; return is; } template ostream &operator<<(ostream &os, vector &A) { for (size_t i = 0; i < A.size(); i++) { os << A[i]; if (i != A.size() - 1) os << ' '; } return os; } // vector> template istream &operator>>(istream &is, vector> &A) { for (auto &a : A) is >> a; return is; } template ostream &operator<<(ostream &os, vector> &A) { for (size_t i = 0; i < A.size(); i++) { os << A[i]; if (i != A.size() - 1) os << endl; } return os; } // pair template istream &operator>>(istream &is, pair &A) { is >> A.first >> A.second; return is; } template ostream &operator<<(ostream &os, pair &A) { os << A.first << ' ' << A.second; return os; } // vector> template istream &operator>>(istream &is, vector> &A) { for (size_t i = 0; i < A.size(); i++) { is >> A[i]; } return is; } template ostream &operator<<(ostream &os, vector> &A) { for (size_t i = 0; i < A.size(); i++) { os << A[i]; if (i != A.size() - 1) os << endl; } return os; } // tuple template struct TuplePrint { static ostream &print(ostream &os, const T &t) { TuplePrint::print(os, t); os << ' ' << get(t); return os; } }; template struct TuplePrint { static ostream &print(ostream &os, const T &t) { os << get<0>(t); return os; } }; template ostream &operator<<(ostream &os, const tuple &t) { TuplePrint::print(os, t); return os; } // io functions void FLUSH() { cout << flush; } void print() { cout << endl; } template void print(Head &&head, Tail &&...tail) { cout << head; if (sizeof...(Tail)) cout << spa; print(forward(tail)...); } template void prisep(vector &A, S sep) { int n = A.size(); for (int i = 0; i < n; i++) { cout << A[i]; if (i != n - 1) cout << sep; } cout << endl; } template void priend(T A, S end) { cout << A << end; } template void prispa(T A) { priend(A, spa); } template bool printif(bool f, T A, S B) { if (f) print(A); else print(B); return f; } template void inp(T &...a) { (cin >> ... >> a); } } // namespace io using namespace io; // read graph vector> read_edges(int n, int m, bool direct = false, int indexed = 1) { vector> edges(n, vector()); for (int i = 0; i < m; i++) { INT(u, v); u -= indexed; v -= indexed; edges[u].push_back(v); if (!direct) edges[v].push_back(u); } return edges; } vector> read_tree(int n, int indexed = 1) { return read_edges(n, n - 1, false, indexed); } template vector>> read_wedges(int n, int m, bool direct = false, int indexed = 1) { vector>> edges(n, vector>()); for (int i = 0; i < m; i++) { INT(u, v); T w; inp(w); u -= indexed; v -= indexed; edges[u].push_back({v, w}); if (!direct) edges[v].push_back({u, w}); } return edges; } template vector>> read_wtree(int n, int indexed = 1) { return read_wedges(n, n - 1, false, indexed); } // yes / no namespace yesno { // yes inline bool yes(bool f = true) { cout << (f ? "yes" : "no") << endl; return f; } inline bool Yes(bool f = true) { cout << (f ? "Yes" : "No") << endl; return f; } inline bool YES(bool f = true) { cout << (f ? "YES" : "NO") << endl; return f; } // no inline bool no(bool f = true) { cout << (!f ? "yes" : "no") << endl; return f; } inline bool No(bool f = true) { cout << (!f ? "Yes" : "No") << endl; return f; } inline bool NO(bool f = true) { cout << (!f ? "YES" : "NO") << endl; return f; } // possible inline bool possible(bool f = true) { cout << (f ? "possible" : "impossible") << endl; return f; } inline bool Possible(bool f = true) { cout << (f ? "Possible" : "Impossible") << endl; return f; } inline bool POSSIBLE(bool f = true) { cout << (f ? "POSSIBLE" : "IMPOSSIBLE") << endl; return f; } // impossible inline bool impossible(bool f = true) { cout << (!f ? "possible" : "impossible") << endl; return f; } inline bool Impossible(bool f = true) { cout << (!f ? "Possible" : "Impossible") << endl; return f; } inline bool IMPOSSIBLE(bool f = true) { cout << (!f ? "POSSIBLE" : "IMPOSSIBLE") << endl; return f; } // Alice Bob inline bool Alice(bool f = true) { cout << (f ? "Alice" : "Bob") << endl; return f; } inline bool Bob(bool f = true) { cout << (f ? "Bob" : "Alice") << endl; return f; } // Takahashi Aoki inline bool Takahashi(bool f = true) { cout << (f ? "Takahashi" : "Aoki") << endl; return f; } inline bool Aoki(bool f = true) { cout << (f ? "Aoki" : "Takahashi") << endl; return f; } } // namespace yesno using namespace yesno; } // namespace templates using namespace templates; template struct Modint { int x; Modint() : x(0) {} Modint(int64_t y) { if (y >= 0) x = y % MOD; else x = (y % MOD + MOD) % MOD; } Modint &operator+=(const Modint &p) { x += p.x; if (x >= MOD) x -= MOD; return *this; } Modint &operator-=(const Modint &p) { x -= p.x; if (x < 0) x += MOD; return *this; } Modint &operator*=(const Modint &p) { x = int(1LL * x * p.x % MOD); return *this; } Modint &operator/=(const Modint &p) { *this *= p.inverse(); return *this; } Modint &operator%=(const Modint &p) { assert(p.x == 0); return *this; } Modint operator-() const { return Modint(-x); } Modint &operator++() { x++; if (x == MOD) x = 0; return *this; } Modint &operator--() { if (x == 0) x = MOD; x--; return *this; } Modint operator++(int) { Modint result = *this; ++*this; return result; } Modint operator--(int) { Modint result = *this; --*this; return result; } friend Modint operator+(const Modint &lhs, const Modint &rhs) { return Modint(lhs) += rhs; } friend Modint operator-(const Modint &lhs, const Modint &rhs) { return Modint(lhs) -= rhs; } friend Modint operator*(const Modint &lhs, const Modint &rhs) { return Modint(lhs) *= rhs; } friend Modint operator/(const Modint &lhs, const Modint &rhs) { return Modint(lhs) /= rhs; } friend Modint operator%(const Modint &lhs, const Modint &rhs) { assert(rhs.x == 0); return Modint(lhs); } bool operator==(const Modint &p) const { return x == p.x; } bool operator!=(const Modint &p) const { return x != p.x; } bool operator<(const Modint &rhs) const { return x < rhs.x; } bool operator<=(const Modint &rhs) const { return x <= rhs.x; } bool operator>(const Modint &rhs) const { return x > rhs.x; } bool operator>=(const Modint &rhs) const { return x >= rhs.x; } Modint inverse() const { int a = x, b = MOD, u = 1, v = 0, t; while (b > 0) { t = a / b; a -= t * b; u -= t * v; std::swap(a, b); std::swap(u, v); } return Modint(u); } Modint pow(int64_t k) const { Modint ret(1); Modint y(x); while (k > 0) { if (k & 1) ret *= y; y *= y; k >>= 1; } return ret; } friend std::ostream &operator<<(std::ostream &os, const Modint &p) { return os << p.x; } friend std::istream &operator>>(std::istream &is, Modint &p) { int64_t y; is >> y; p = Modint(y); return (is); } static int get_mod() { return MOD; } }; struct Arbitrary_Modint { int x; static int MOD; static void set_mod(int mod) { MOD = mod; } Arbitrary_Modint() : x(0) {} Arbitrary_Modint(int64_t y) { if (y >= 0) x = y % MOD; else x = (y % MOD + MOD) % MOD; } Arbitrary_Modint &operator+=(const Arbitrary_Modint &p) { x += p.x; if (x >= MOD) x -= MOD; return *this; } Arbitrary_Modint &operator-=(const Arbitrary_Modint &p) { x -= p.x; if (x < 0) x += MOD; return *this; } Arbitrary_Modint &operator*=(const Arbitrary_Modint &p) { x = int(1LL * x * p.x % MOD); return *this; } Arbitrary_Modint &operator/=(const Arbitrary_Modint &p) { *this *= p.inverse(); return *this; } Arbitrary_Modint &operator%=(const Arbitrary_Modint &p) { assert(p.x == 0); return *this; } Arbitrary_Modint operator-() const { return Arbitrary_Modint(-x); } Arbitrary_Modint &operator++() { x++; if (x == MOD) x = 0; return *this; } Arbitrary_Modint &operator--() { if (x == 0) x = MOD; x--; return *this; } Arbitrary_Modint operator++(int) { Arbitrary_Modint result = *this; ++*this; return result; } Arbitrary_Modint operator--(int) { Arbitrary_Modint result = *this; --*this; return result; } friend Arbitrary_Modint operator+(const Arbitrary_Modint &lhs, const Arbitrary_Modint &rhs) { return Arbitrary_Modint(lhs) += rhs; } friend Arbitrary_Modint operator-(const Arbitrary_Modint &lhs, const Arbitrary_Modint &rhs) { return Arbitrary_Modint(lhs) -= rhs; } friend Arbitrary_Modint operator*(const Arbitrary_Modint &lhs, const Arbitrary_Modint &rhs) { return Arbitrary_Modint(lhs) *= rhs; } friend Arbitrary_Modint operator/(const Arbitrary_Modint &lhs, const Arbitrary_Modint &rhs) { return Arbitrary_Modint(lhs) /= rhs; } friend Arbitrary_Modint operator%(const Arbitrary_Modint &lhs, const Arbitrary_Modint &rhs) { assert(rhs.x == 0); return Arbitrary_Modint(lhs); } bool operator==(const Arbitrary_Modint &p) const { return x == p.x; } bool operator!=(const Arbitrary_Modint &p) const { return x != p.x; } bool operator<(const Arbitrary_Modint &rhs) { return x < rhs.x; } bool operator<=(const Arbitrary_Modint &rhs) { return x <= rhs.x; } bool operator>(const Arbitrary_Modint &rhs) { return x > rhs.x; } bool operator>=(const Arbitrary_Modint &rhs) { return x >= rhs.x; } Arbitrary_Modint inverse() const { int a = x, b = MOD, u = 1, v = 0, t; while (b > 0) { t = a / b; a -= t * b; u -= t * v; std::swap(a, b); std::swap(u, v); } return Arbitrary_Modint(u); } Arbitrary_Modint pow(int64_t k) const { Arbitrary_Modint ret(1); Arbitrary_Modint y(x); while (k > 0) { if (k & 1) ret *= y; y *= y; k >>= 1; } return ret; } friend std::ostream &operator<<(std::ostream &os, const Arbitrary_Modint &p) { return os << p.x; } friend std::istream &operator>>(std::istream &is, Arbitrary_Modint &p) { int64_t y; is >> y; p = Arbitrary_Modint(y); return (is); } static int get_mod() { return MOD; } }; int Arbitrary_Modint::MOD = 998244353; using modint9 = Modint<998244353>; using modint1 = Modint<1000000007>; using modint = Arbitrary_Modint; using mint = modint9; struct UnionFind { int n; std::vector par; int group; UnionFind() = default; UnionFind(int n) : n(n) { par.assign(n, -1); group = n; } int find(int x) { if (par[x] < 0) return x; par[x] = find(par[x]); return par[x]; } bool unite(int x, int y) { x = find(x); y = find(y); if (x == y) return false; if (par[x] > par[y]) std::swap(x, y); group--; par[x] += par[y]; par[y] = x; return true; } bool same(int x, int y) { return find(x) == find(y); } int size(int x) { return -par[find(x)]; } std::vector roots() { std::vector ret; for (int i = 0; i < n; i++) { if (i == find(i)) ret.push_back(i); } return ret; } }; struct Namori { int n; int logn; std::vector> edges; std::vector circle; std::vector depth; std::vector tree; std::vector> par; Namori() = default; Namori(int n) : n(n) { edges.resize(n); depth.assign(n, -1); tree.assign(n, -1); logn = -1; }; void add_edge(int u, int v) { edges[u].push_back(v); edges[v].push_back(u); } void read_edges(int indexed = 1) { int u, v; for (int i = 0; i < n; i++) { std::cin >> u >> v; u -= indexed; v -= indexed; edges[u].push_back(v); edges[v].push_back(u); } } void build() { UnionFind UF(n); int uu = -1, vv = -1; for (int u = 0; u < n; u++) { for (auto v : edges[u]) { if (u > v) continue; if (!UF.unite(u, v)) { uu = u; vv = v; break; }; } } int u = uu; int v = vv; std::vector bef(n, -1); std::stack st; st.push(u); while (!st.empty()) { int pos = st.top(); st.pop(); for (auto npos : edges[pos]) { if (bef[npos] != -1 || (pos == u && npos == v)) continue; bef[npos] = pos; if (npos == v) { while (!st.empty()) st.pop(); break; } st.push(npos); } } circle.push_back(v); depth[v] = 0; st.push(v); tree[v] = 0; if (bef[v] == -1) bef[v] = u; while (v != u) { v = bef[v]; depth[v] = 0; tree[v] = circle.size(); circle.push_back(v); st.push(v); } while (!st.empty()) { int pos = st.top(); st.pop(); for (auto npos : edges[pos]) { if (depth[npos] == -1) { depth[npos] = depth[pos] + 1; tree[npos] = tree[pos]; st.push(npos); } } } } bool isroot(int u) { return u == circle[tree[u]]; } bool same_tree(int u, int v) { return tree[u] == tree[v]; } void lca_build() { logn = 0; while ((1 << logn) < n) logn++; par.assign(logn, std::vector(n, -1)); std::stack st; for (auto pos : circle) st.push(pos); while (!st.empty()) { int pos = st.top(); st.pop(); for (auto npos : edges[pos]) { if (depth[npos] > depth[pos]) { par[0][npos] = pos; st.push(npos); } } } for (int i = 1; i < logn; i++) { for (int j = 0; j < n; j++) { int p = par[i - 1][j]; if (p != -1) { par[i][j] = par[i - 1][p]; } } } } int lca(int u, int v) { if (logn == -1) lca_build(); if (depth[u] > depth[v]) std::swap(u, v); int d = depth[v] - depth[u]; int i = 0; while (d > 0) { if (d & 1) v = par[i][v]; d >>= 1; i++; } if (u == v) return u; for (int i = logn - 1; i >= 0; i--) { int pu = par[i][u]; int pv = par[i][v]; if (pu != pv) { u = pu; v = pv; } } return par[0][u]; } int dist(int u, int v) { if (tree[u] == tree[v]) { int p = lca(u, v); return depth[u] + depth[v] - 2 * depth[p]; } else { int d = abs(tree[u] - tree[v]); d = std::min(d, (int)circle.size() - d); return depth[u] + depth[v] + d; } } }; template struct Matrix { int n, m; std::vector> A; Matrix() = default; Matrix(int n, int m) : n(n), m(m), A(n, std::vector(m, 0)) {} Matrix(int n) : n(n), m(n), A(n, std::vector(n, 0)) {} Matrix(std::vector> A) : n(A.size()), m(A[0].size()), A(A) {} inline const std::vector &operator[](int k) const { return (A.at(k)); } inline std::vector &operator[](int k) { return (A.at(k)); } Matrix T() { Matrix B(m, n); for (int i = 0; i < m; i++) for (int j = 0; j < n; j++) { B.A[i][j] = A[j][i]; } return B; } Matrix &operator+=(const Matrix &B) { assert(n == int(B.A.size())); assert(m == int(B.A[0].size())); for (int i = 0; i < n; i++) for (int j = 0; j < m; j++) { this->A[i][j] += B[i][j]; } return *this; } Matrix &operator-=(const Matrix &B) { assert(n == int(B.A.size())); assert(m == int(B.A[0].size())); for (int i = 0; i < n; i++) for (int j = 0; j < m; j++) { this->A[i][j] -= B[i][j]; } return *this; } Matrix &operator*=(const Matrix &B) { int k = B[0].size(); assert(m == int(B.A.size())); std::vector> C(n, std::vector(k, 0)); for (int i = 0; i < n; i++) for (int j = 0; j < k; j++) { for (int l = 0; l < m; l++) { C[i][j] += this->A[i][l] * B[l][j]; } } swap(this->A, C); return *this; } template Matrix &operator*=(const Ti x) { for (auto &row : A) { for (auto &e : row) { e *= x; } } return *this; } Matrix operator-() { return (Matrix(*this) *= -1); } Matrix operator+(const Matrix &B) const { return (Matrix(*this) += B); } Matrix operator-(const Matrix &B) const { return (Matrix(*this) -= B); } Matrix operator*(const Matrix &B) const { return (Matrix(*this) *= B); } type det() { auto arr = A; assert(n == m); type ret = 1; for (int i = 0; i < n; i++) { if (arr[i][i] == 0) { bool ng = true; for (int j = i + 1; j < n; j++) { if (arr[j][i] == 0) continue; swap(arr[i], arr[j]); ret *= -1; ng = false; break; } if (ng) return 0; } ret *= arr[i][i]; type inv = type(1) / arr[i][i]; for (int j = i; j < n; j++) arr[i][j] *= inv; for (int j = i + 1; j < n; j++) { type x = arr[j][i]; for (int k = i; k < n; k++) { arr[j][k] -= arr[i][k] * x; } } } return ret; } void I() { assert(n == m); for (int i = 0; i < n; i++) { for (int j = 0; j < m; j++) { if (i == j) A[i][j] = 1; else A[i][j] = 0; } } } Matrix inv() { assert(n == m); Matrix ret(n); ret.I(); auto &B = ret.A; auto arr = A; for (int j = 0; j < n; j++) { int ii = -1; for (int i = j; i < n; i++) { if (arr[i][j] != 0) { ii = i; break; } } if (ii == -1) { return {}; } swap(arr[j], arr[ii]); swap(B[j], B[ii]); ii = j; type inv = type(1) / arr[ii][j]; for (int jj = 0; jj < n; jj++) { B[ii][jj] *= inv; arr[ii][jj] *= inv; } for (int i = 0; i < n; i++) { if (i == ii) continue; type t = arr[i][j]; for (int jj = 0; jj < n; jj++) { arr[i][jj] -= arr[ii][jj] * t; B[i][jj] -= B[ii][jj] * t; } } } return ret; } int choose_pivot(int h, int c) const { for (int j = h; j < n; j++) { if (A[j][c] != type(0)) return j; } return -1; } friend std::ostream &operator<<(std::ostream &os, const Matrix &p) { for (int i = 0; i < p.n; i++) { for (auto &x : p.A[i]) { os << x << " "; } if (i != p.n - 1) { os << "\n"; } } return (os); } friend std::istream &operator>>(std::istream &is, Matrix &p) { for (auto &row : p.A) { for (auto &x : row) { is >> x; } } return (is); } }; template Matrix Matrix_exp(Matrix A, Matrix B, long long k) { assert(A.A.size() == A[0].size()); assert(A.A.size() == B.A.size()); assert(B.A[0].size() == 1u); while (k > 0) { if (k & 1) B = A * B; A *= A; k >>= 1; } return B; } void solve() { INT(n, k); Namori G(n); G.read_edges(); G.build(); int c = G.circle.size(); Matrix A(2, 2), B(2, 1); A[0][0] = 0; A[0][1] = 1; A[1][0] = k - 1; A[1][1] = k - 2; B[0][0] = k; auto C = Matrix_exp(A, B, c - 1); mint ans = C[1][0]; ans *= mint(k - 1).pow(n - c); print(ans); } int main() { cin.tie(0)->sync_with_stdio(0); // cout << fixed << setprecision(12); int t; t = 1; // cin >> t; while (t--) solve(); return 0; }