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#include <bits/stdc++.h>

using namespace std;
using LL = long long;

const int MAXN = 3003;
const int MOD = 1000000007;

LL n, m;

LL dp[MAXN][MAXN][2];

int power(long long x, unsigned int y)
{
  int res = 1;
  x = x % MOD;

  if (x == 0) return 0;

  while (y > 0) {
    if (y & 1)
      res = (res*x) % MOD;

    y = y>>1;
    x = (x*x) % MOD;
  }
  return res;
}

LL depe(LL n, LL k, bool b) {
  if (k > m) {
    return 0;
  }
  if (n == 0) {
    return 1;
  }

  if (dp[n][k][b] != -1) {
    return dp[n][k][b];
  }

  if (b == 0) {
    int x = depe(n - 1, k, 0) * max(0LL, (m - k)) % MOD;
    int y = depe(n - 1, k, 1) * k % MOD;
    int sum = (x + y) % MOD;
    dp[n][k][b] = sum;
  } else {
    int x = depe(n - 1, k, 1) * k % MOD;
    int y = depe(n - 1, k + 1, 0) * max(0LL, (m - k - 1LL)) % MOD;
    int sum = (x + y) % MOD;
    dp[n][k][b] = sum;
  }

  // cout << "depe " << n << " " << k << " " << b << " " << dp[n][k][b] << endl;
  return dp[n][k][b];
}

int main() {
  cin >> n >> m;
  if (n == 1) {
    cout << 0 << endl;
    return 0;
  }
  if (n == 2) {
    cout << m << endl;
    return 0;
  }
  memset(dp, -1, sizeof(dp));
  
  int sum = depe(n - 2, 1, 0);
  LL mpo2 = (m * (m - 1) / 2) % MOD;
  mpo2 *= 2;
  mpo2 %= MOD;

  LL res = power(m, n - 2) - sum;
  if (res < 0) {
    res += MOD;
  }

  res *= mpo2;
  res %= MOD;
  LL pom = m * (LL)power(m, n - 2) % MOD;
  res += pom;
  res %= MOD;
  cout << res << endl;
}