#line 1 "combined.cpp" #pragma region Macros #include using namespace std; template inline bool chmax(T &a, T b) { if(a < b) { a = b; return 1; } return 0; } template inline bool chmin(T &a, T b) { if(a > b) { a = b; return 1; } return 0; } #ifdef DEBUG template ostream &operator<<(ostream &os, const pair &p) { os << '(' << p.first << ',' << p.second << ')'; return os; } template ostream &operator<<(ostream &os, const vector &v) { os << '{'; for(int i = 0; i < (int)v.size(); i++) { if(i) { os << ','; } os << v[i]; } os << '}'; return os; } void debugg() { cerr << endl; } template void debugg(const T &x, const Args &... args) { cerr << " " << x; debugg(args...); } #define debug(...) \ cerr << __LINE__ << " [" << #__VA_ARGS__ << "]: ", debugg(__VA_ARGS__) #define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl #else #define debug(...) (void(0)) #define dump(x) (void(0)) #endif struct Setup { Setup() { cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(15); } } __Setup; using ll = long long; #define OVERLOAD3(_1, _2, _3, name, ...) name #define ALL(v) (v).begin(), (v).end() #define RALL(v) (v).rbegin(), (v).rend() #define REP1(i, n) for(int i = 0; i < int(n); i++) #define REP2(i, a, b) for(int i = (a); i < int(b); i++) #define REP(...) OVERLOAD3(__VA_ARGS__, REP2, REP1)(__VA_ARGS__) #define UNIQUE(v) sort(ALL(v)), (v).erase(unique(ALL(v)), (v).end()) #define REVERSE(v) reverse(ALL(v)) #define SZ(v) ((int)(v).size()) const int INF = 1 << 30; const ll LLINF = 1LL << 60; constexpr int MOD = 1000000007; constexpr int MOD2 = 998244353; const int dx[4] = {1, 0, -1, 0}; const int dy[4] = {0, -1, 0, 1}; void Case(int i) { cout << "Case #" << i << ": "; } int popcount(int x) { return __builtin_popcount(x); } ll popcount(ll x) { return __builtin_popcountll(x); } #pragma endregion Macros #line 2 "/Users/siro53/kyo-pro/compro_library/modint/modint.hpp" #line 6 "/Users/siro53/kyo-pro/compro_library/modint/modint.hpp" template class ModInt { public: ModInt() : x(0) {} ModInt(long long y) : x(y >= 0 ? y % umod() : (umod() - (-y) % umod()) % umod()) {} unsigned int val() const { return x; } ModInt &operator+=(const ModInt &p) { if((x += p.x) >= umod()) x -= umod(); return *this; } ModInt &operator-=(const ModInt &p) { if((x += umod() - p.x) >= umod()) x -= umod(); return *this; } ModInt &operator*=(const ModInt &p) { x = (unsigned int)(1ULL * x * p.x % umod()); return *this; } ModInt &operator/=(const ModInt &p) { *this *= p.inv(); return *this; } ModInt operator-() const { return ModInt(-(long long)x); } ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; } ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; } ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; } ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; } bool operator==(const ModInt &p) const { return x == p.x; } bool operator!=(const ModInt &p) const { return x != p.x; } ModInt inv() const { long long a = x, b = mod, u = 1, v = 0, t; while(b > 0) { t = a / b; std::swap(a -= t * b, b); std::swap(u -= t * v, v); } return ModInt(u); } ModInt pow(unsigned long long n) const { ModInt ret(1), mul(x); while(n > 0) { if(n & 1) ret *= mul; mul *= mul; n >>= 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 &a) { long long t; is >> t; a = ModInt(t); return (is); } static constexpr int get_mod() { return mod; } private: unsigned int x; static constexpr unsigned int umod() { return mod; } }; #line 78 "combined.cpp" using mint = ModInt; void solve() { int N, K; cin >> N >> K; vector dp(K+1, vector(N+1, 0)); dp[0][0] = 1; REP(i, K) { REP(j, N+1) { if(j > 0) dp[i+1][j-1] += dp[i][j] * j; if(j < N) dp[i+1][j+1] += dp[i][j] * (N - j); } } mint ans = 0; REP(j, N+1) if((K - j) % 2 == 0) { int y = (K - j) / 2; ans += mint(N + y) * dp[K][j] / mint(N).pow(K); } cout << ans << endl; } int main() { int T{1}; // cin >> T; while(T--) solve(); }