#define CPP17 #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #ifdef CPP17 #include #endif #define endl codeforces #define ALL(v) std::begin(v), std::end(v) #define ALLR(v) std::rbegin(v), std::rend(v) using ll = std::int64_t; using ull = std::uint64_t; using pii = std::pair; using tii = std::tuple; using pll = std::pair; using tll = std::tuple; using size_type = ssize_t; template using vec = std::vector; template using vvec = vec>; template const T& var_min(const T &t) { return t; } template const T& var_max(const T &t) { return t; } template const T& var_min(const T &t, const Tail&... tail) { return std::min(t, var_min(tail...)); } template const T& var_max(const T &t, const Tail&... tail) { return std::max(t, var_max(tail...)); } template void chmin(T &t, const Tail&... tail) { t = var_min(t, tail...); } template void chmax(T &t, const Tail&... tail) { t = var_max(t, tail...); } template struct multi_dim_array { using type = std::array::type, Head>; }; template struct multi_dim_array { using type = std::array; }; template using mdarray = typename multi_dim_array::type; #ifdef CPP17 template void fill_seq(T &t, F f, Args... args) { if constexpr (std::is_invocable::value) { t = f(args...); } else { for (size_type i = 0; i < t.size(); i++) fill_seq(t[i], f, args..., i); } } #endif template vec make_v(size_type sz) { return vec(sz); } template auto make_v(size_type hs, Tail&&... ts) { auto v = std::move(make_v(std::forward(ts)...)); return vec(hs, v); } namespace init__ { struct InitIO { InitIO() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << std::fixed << std::setprecision(30); } } init_io; } template T ceil_pow2(T bound) { T ret = 1; while (ret < bound) ret *= 2; return ret; } template T ceil_div(T a, T b) { return a / b + !!(a % b); } #define CPP17 namespace math { template constexpr T pow(const T &n, ll k) { T ret = n.mul_id_ele(); T cur = n; while (k) { if (k & 1) ret *= cur; cur *= cur; k /= 2; } return ret; } } namespace math { template struct Modint { constexpr Modint(ll x) noexcept : x(static_cast((Mod + x % Mod) % Mod)) { } constexpr Modint() noexcept : Modint(0) { } constexpr Modint add_id_ele() const noexcept { return Modint(0); } constexpr Modint mul_id_ele() const noexcept { return Modint(1); } constexpr ll value() const noexcept { return static_cast(x); } constexpr Modint& operator+=(const Modint &oth) noexcept { x += oth.value(); if (Mod <= x) x -= Mod; return *this; } constexpr Modint& operator-=(const Modint &oth) noexcept { x += Mod - oth.value(); if (Mod <= x) x -= Mod; return *this; } constexpr Modint& operator*=(const Modint &oth) noexcept { x *= oth.value(); x %= Mod; return *this; } constexpr Modint& operator/=(const Modint &oth) noexcept { x *= oth.inv().value(); x %= Mod; return *this; } constexpr Modint operator+(const Modint &oth) const noexcept { return Modint(x) += oth; } constexpr Modint operator-(const Modint &oth) const noexcept { return Modint(x) -= oth; } constexpr Modint operator*(const Modint &oth) const noexcept { return Modint(x) *= oth; } constexpr Modint operator/(const Modint &oth) const noexcept { return Modint(x) /= oth; } constexpr Modint operator-() const noexcept { return Modint((x != 0) * (Mod - x)); } constexpr bool operator==(const Modint &oth) const noexcept { return value() == oth.value(); } template constexpr typename std::enable_if::value, const Modint&>::type operator=(T t) noexcept { (*this) = Modint(std::forward(t)); return *this; } constexpr Modint inv() const noexcept { return ::math::pow(*this, Mod - 2); } constexpr ll mod() const noexcept { return static_cast(Mod); } private: ll x; }; template Modint inv(Modint m) { m.inv(); return m; } template std::istream& operator>>(std::istream &is, Modint &m) { ll v; is >> v; m = v; return is; } template std::ostream& operator<<(std::ostream &os, Modint m) { os << m.value(); return os; } } constexpr ll mod = 1e9 + 7; using mint = math::Modint; const size_type SIZE = 1e6; std::array dp1, dp2; int main() { ll n, k; std::cin >> n >> k; dp1[0] = dp2[0] = 1; mint sum = k; sum *= k + 1; sum /= 2; for (ll i = 0; i < n; i++) { dp1[i + 1] = dp1[i] * (sum + k); dp2[i + 1] = dp2[i] * sum; } std::cout << (dp1[n] - dp2[n]) << "\n"; return 0; }