Problem: Once, during a lesson, Sasha got bored and decided to talk with his friends. Suddenly, he saw Kefa. Since we can talk endlessly about Kefa, we won't even start doing that. The conversation turned to graphs. Kefa promised Sasha to tell him about one interesting fact from graph theory if Sasha helps Kefa to count the number of beautiful trees. 

In this task, a tree is a weighted connected graph, consisting of n vertices and n-1 edges, and weights of edges are integers from 1 to m. Kefa determines the beauty of a tree as follows: he finds in the tree his two favorite vertices — vertices with numbers a and b, and counts the distance between them. The distance between two vertices x and y is the sum of weights of edges on the simple path from x to y. If the distance between two vertices a and b is equal to m, then the tree is beautiful.

Sasha likes graph theory, and even more, Sasha likes interesting facts, that's why he agreed to help Kefa. Luckily, Sasha is familiar with you the best programmer in Byteland. Help Sasha to count the number of beautiful trees for Kefa. Two trees are considered to be distinct if there is an edge that occurs in one of them and doesn't occur in the other one. Edge's weight matters.

Kefa warned Sasha, that there can be too many beautiful trees, so it will be enough to count the number modulo 10^9 + 7.

Input

The first line contains four integers n, m, a, b (2 ≤ n ≤ 10^6, 1 ≤ m ≤ 10^6, 1 ≤ a, b ≤ n, a ≠ b) — the number of vertices in the tree, the maximum weight of an edge and two Kefa's favorite vertices.

Output

Print one integer — the number of beautiful trees modulo 10^9+7.

Examples

Input


3 2 1 3


Output


5


Input


3 1 1 2


Output


2


Input


5 15 1 5


Output


345444

Note

There are 5 beautiful trees in the first example:

<image>

In the second example the following trees are beautiful:

<image>

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;
const long long maxx = 790;
const long long maxn = 1000000 + 7;
const long long mod = 1e9 + 7;
const long long maxs = 500000 + 7;
const long long maxm = 400000 + 7;
const long long maxk = 1008 + 7;
const long long maxw = 100 + 7;
const long long maxh = 100 + 7;
const double pi = 3.1415926;
const long long ten = 10;
const long long ooi = 1e9 + 7;
const long long ool = 1e18 + 7;
const long double eps = 1e-8;
const int apsz = 26;
long long n, m;
long long p[maxn];
long long cn[maxn];
long long cm[maxn];
long long qm[maxn];
long long inv[maxn];
long long f[maxn];
long long limit = 0;
long long qw(long long a, long long b) {
  long long ans = 1;
  while (b) {
    if (b & 1) {
      ans *= a;
      ans %= mod;
    }
    b >>= 1;
    a *= a;
    a %= mod;
  }
  if (ans > mod) ans %= mod;
  return ans;
}
void init() {
  int a, b;
  cin >> n >> m >> a >> b;
  f[0] = 1;
  for (int i = (1); i <= (max(n, m)); i++) f[i] = f[i - 1] * i, f[i] %= mod;
  qm[0] = 1;
  for (int i = (1); i <= (max(n, m)); i++) qm[i] = qm[i - 1] * m, qm[i] %= mod;
  long long now = qw(f[max(n, m)], mod - 2);
  for (long long i = (max(n, m)); i >= (1); i--) {
    inv[i] = now * f[i - 1] % mod;
    now *= i;
    now %= mod;
  }
  cm[0] = cn[0] = 1;
  limit = min(n - 2, m - 1);
  for (int i = (0); i <= (m - 1); i++)
    cm[i + 1] = cm[i] * (m - 1 - i), cm[i + 1] %= mod, cm[i + 1] *= inv[i + 1],
           cm[i + 1] %= mod;
  for (int i = (0); i <= (n - 2); i++)
    cn[i + 1] = cn[i] * (n - 2 - i) % mod,
           cn[i + 1] = cn[i + 1] * inv[i + 1] % mod;
}
long long mycal(long long i) {
  long long yu1 = n - i - 2;
  yu1++;
  long long wgr = i + 2;
  long long ans;
  if (yu1 == 1)
    return ans = 1;
  else
    return ans = wgr * qw(n, yu1 - 2) % mod;
}
void solve() {
  long long ans = 0;
  for (int i = (0); i <= (n - 2); i++) {
    if (i > m - 1) break;
    long long tp = cn[i] * cm[i] % mod;
    tp *= f[i], tp %= mod;
    tp *= qm[n - i - 2];
    tp %= mod;
    tp *= mycal(i);
    tp %= mod;
    ans += tp;
    ans %= mod;
  }
  cout << ans << endl;
}
int main(void) {
  ios::sync_with_stdio(false);
  cout.tie(0);
  cin.tie(0);
  init();
  solve();
  return 0;
}