func_code_string: #include <bits/stdc++.h>   using namespace std;   const int mod = 1e9 + 7;   inline long long read() {     long long x = 0, f = 1;     char c = getchar();     while (c <  0  || c >  9 ) {       if (c ==  - ) f = -1;       c = getchar();     }     while (c >=  0  && c <=  9 ) {       x = (x << 1) + (x << 3) + c -  0 ;       c = getchar();     }     return x * f;   }   int n, m, fac[1000100], ifac[1000100], ans;   int qpow(int a, int b) {     int ans = 1;     while (b) {       if (b & 1) ans = 1LL * ans * a % mod;       a = 1LL * a * a % mod;       b >>= 1;     }     return ans;   }   void init(int n) {     fac[0] = 1;     for (int i = 1; i <= n; ++i) {       fac[i] = 1LL * fac[i - 1] * i % mod;     }     ifac[n] = qpow(fac[n], mod - 2);     for (int i = n - 1; i >= 0; --i) {       ifac[i] = 1LL * ifac[i + 1] * (i + 1) % mod;     }   }   inline int C(int n, int m) {     if (n < m) return 0;     return 1LL * fac[n] * ifac[m] % mod * ifac[n - m] % mod;   }   int main() {     n = read(), m = read();     read(), read();     init(max(n, m));     ans = 1LL * fac[n - 2] * C(m - 1, n - 2) % mod;     for (int i = 1; i < n - 1; ++i) {       ans = (ans + 1LL * C(m - 1, i - 1) * qpow(m, n - i - 1) % mod *                        C(n - 2, i - 1) % mod * fac[i - 1] % mod * (i + 1) % mod *                        qpow(n, n - i - 2)) %             mod;     }     printf( %d n , ans);     return 0;   }   