#include<bits/stdc++.h>

#define LL long long

#define LD long double

#define ull unsigned long long

#define fi first

#define se second

#define mk make_pair

#define PLL pair<LL, LL>

#define PLI pair<LL, int>

#define PII pair<int, int>

#define SZ(x) ((int)x.size())

#define ALL(x) (x).begin(), (x).end()

#define fio ios::sync_with_stdio(false); cin.tie(0);

using namespace std;

const int N = 1e6 + ;

const int inf = 0x3f3f3f3f;

const LL INF = 0x3f3f3f3f3f3f3f3f;

const int mod = 1e9 + ;

const double eps = 1e-;

const double PI = acos(-);

template<class T, class S> inline void add(T& a, S b) {a += b; if(a >= mod) a -= mod;}

template<class T, class S> inline void sub(T& a, S b) {a -= b; if(a < ) a += mod;}

template<class T, class S> inline bool chkmax(T& a, S b) {return a < b ? a = b, true : false;}

template<class T, class S> inline bool chkmin(T& a, S b) {return a > b ? a = b, true : false;}

int power(int a, int b) {

    int ans = ;

    while(b) {

        if(b & ) ans = 1LL * ans * a % mod;

        a = 1LL * a * a % mod; b >>= ;

    }

    return ans;

}

int F[N], Finv[N], inv[N];

int C(int n, int m) {

    if(n <  || n < m) return ;

    return 1LL * F[n] * Finv[m] % mod * Finv[n - m] % mod;

}

int n, m, a, b;

int main() {

    inv[] = F[] = Finv[] = ;

    for(int i = ; i < N; i++) inv[i] = 1LL * (mod - mod / i) * inv[mod % i] % mod;

    for(int i = ; i < N; i++) F[i] = 1LL * F[i - ] * i % mod;

    for(int i = ; i < N; i++) Finv[i] = 1LL * Finv[i - ] * inv[i] % mod;

    scanf("%d%d%d%d", &n, &m, &a, &b);

    int ans = ;

    for(int i = ; i <= n; i++) {

        if(i < n) add(ans, 1LL * C(n - , i - ) * F[i - ] % mod * C(m - , i - ) % mod * power(m, n - i) % mod * i % mod * power(n, n - i - ) % mod);

        else add(ans, 1LL * F[i - ] * C(m - , i - ) % mod);

    }

    printf("%d\n", ans);

    return ;

}

/*

*/