#include using namespace std; #define REP(i,n) for(ll i=0;i<(ll)n;i++) #define dump(x) cerr << "Line " << __LINE__ << ": " << #x << " = " << (x) << "\n"; #define spa << " " << #define fi first #define se second #define ALL(a) (a).begin(),(a).end() #define ALLR(a) (a).rbegin(),(a).rend() using ld = long double; using ll = long long; using ull = unsigned long long; using pii = pair; using pll = pair; using pdd = pair; template using V = vector; template using P = pair; template vector make_vec(size_t n, T a) { return vector(n, a); } template auto make_vec(size_t n, Ts... ts) { return vector(n, make_vec(ts...)); } template ostream& operator << (ostream& os, const pair v){os << "(" << v.first << ", " << v.second << ")"; return os;} template ostream& operator<<(ostream &os, const vector &v) { for (auto &e : v) os << e << ' '; return os; } template ostream& operator<<(ostream& os, const vector> &v){ for(auto &e : v){os << e << "\n";} return os;} struct fast_ios { fast_ios(){ cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_; template void UNIQUE(vector &x) {sort(ALL(x));x.erase(unique(ALL(x)), x.end());} template bool chmax(T &a, const T &b) { if (a bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; } void fail() { cout << -1 << '\n'; exit(0); } inline int popcount(const int x) { return __builtin_popcount(x); } inline int popcount(const ll x) { return __builtin_popcountll(x); } template void debug(vector>&v,ll h,ll w){for(ll i=0;i void debug(vector&v,ll n){if(n!=0)cerr< class modint { // long long から modint を作るときは必ず正の数にしてからコンストラクタに入れること! // そうしないとバグります using u64 = std::uint_fast64_t; public: u64 a; constexpr modint(const u64 x = 0) noexcept : a(x % Modulus) {} constexpr u64 &value() noexcept { return a; } constexpr const u64 &value() const noexcept { return a; } constexpr modint operator+(const modint rhs) const noexcept { return modint(*this) += rhs; } constexpr modint operator-(const modint rhs) const noexcept { return modint(*this) -= rhs; } constexpr modint operator*(const modint rhs) const noexcept { return modint(*this) *= rhs; } constexpr modint operator/(const modint rhs) const noexcept { return modint(*this) /= rhs; } constexpr modint &operator+=(const modint rhs) noexcept { a += rhs.a; if (a >= Modulus) { a -= Modulus; } return *this; } constexpr modint &operator-=(const modint rhs) noexcept { if (a < rhs.a) { a += Modulus; } a -= rhs.a; return *this; } constexpr modint &operator*=(const modint rhs) noexcept { a = a * rhs.a % Modulus; return *this; } constexpr modint &operator/=(modint rhs) noexcept { u64 exp = Modulus - 2; while (exp) { if (exp % 2) { *this *= rhs; } rhs *= rhs; exp /= 2; } return *this; } }; using mint = modint; using vm = vector; using vvm = vector; ostream& operator << (ostream& os, const mint v){ os << v.value(); return os; } template constexpr T power(T x, U exp) { T ret = static_cast(1); while (exp) { if (exp % static_cast(2) == static_cast(1)) ret *= x; exp /= static_cast(2); x *= x; } return ::std::move(ret); } int main(){ ll N, M; cin >> N >> M; auto pows = make_vec(M+1, mint(0)); REP(i, M+1){ pows[i] = power(mint(i), N-1); } // dump(pows) mint res = 0; for(ll X=1;X<=M;X++){ mint tmp = 0; tmp += pows[X] * X * (X+1); tmp -= pows[X-1] * X * (X-1); tmp -= pows[M-X+1] * (X+M) * (M-X+1); tmp += pows[M-X] * (X+1+M) * (M-X); // dump(tmp) tmp *= X; tmp *= N; tmp /= 2; res += tmp; } cout << res << endl; return 0; }