func_code_string: #include <bits/stdc++.h>   using namespace std;   const int MOD = (int)1e9 + 7;   const int FFTMOD = 119 << 23 | 1;   const int INF = (int)1e9 + 23111992;   const long long LINF = (long long)1e18 + 23111992;   const long double PI = acos((long double)-1);   const long double EPS = 1e-9;   inline long long gcd(long long a, long long b) {     long long r;     while (b) {       r = a % b;       a = b;       b = r;     }     return a;   }   inline long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }   inline long long fpow(long long n, long long k, int p = MOD) {     long long r = 1;     for (; k; k >>= 1) {       if (k & 1) r = r * n % p;       n = n * n % p;     }     return r;   }   template <class T>   inline int chkmin(T& a, const T& val) {     return val < a ? a = val, 1 : 0;   }   template <class T>   inline int chkmax(T& a, const T& val) {     return a < val ? a = val, 1 : 0;   }   inline unsigned long long isqrt(unsigned long long k) {     unsigned long long r = sqrt(k) + 1;     while (r * r > k) r--;     return r;   }   inline long long icbrt(long long k) {     long long r = cbrt(k) + 1;     while (r * r * r > k) r--;     return r;   }   inline void addmod(int& a, int val, int p = MOD) {     if ((a = (a + val)) >= p) a -= p;   }   inline void submod(int& a, int val, int p = MOD) {     if ((a = (a - val)) < 0) a += p;   }   inline int mult(int a, int b, int p = MOD) { return (long long)a * b % p; }   inline int inv(int a, int p = MOD) { return fpow(a, p - 2, p); }   inline int sign(long double x) { return x < -EPS ? -1 : x > +EPS; }   inline int sign(long double x, long double y) { return sign(x - y); }   mt19937 mt(chrono::high_resolution_clock::now().time_since_epoch().count());   inline int myrand() { return abs((int)mt()); }   const int maxn = 2e6 + 5;   int fac[maxn];   int ifac[maxn];   int binom(int a, int b) {     if (a > b) return 0;     return mult(fac[b], mult(ifac[a], ifac[b - a]));   }   void chemthan() {     fac[0] = 1;     for (int i = (1); i < (maxn); ++i) fac[i] = mult(fac[i - 1], i);     for (int i = (0); i < (maxn); ++i) ifac[i] = inv(fac[i]);     int n, m, a, b;     cin >> n >> m >> a >> b;     int res = 0;     for (int k = (1); k < (n); ++k) {       int coef = binom(k - 1, m - 1);       int d = n - 1 - k;       int coef2 = !d ? 1 : mult(n - d, fpow(n, d - 1));       coef = mult(coef, fac[k - 1]);       addmod(res, mult(coef, mult(binom(k - 1, n - 2),                                   mult(coef2, fpow(m, n - k - 1)))));     }     cout << res <<   n ;   }   int main(int argc, char* argv[]) {     ios_base::sync_with_stdio(0), cin.tie(0);     if (argc > 1) {       assert(freopen(argv[1],  r , stdin));     }     if (argc > 2) {       assert(freopen(argv[2],  wb , stdout));     }     chemthan();     cerr <<   nTime elapsed:   << 1000 * clock() / CLOCKS_PER_SEC <<  ms n ;     return 0;   }   