#include <iostream>
#include <cstring>

using namespace std;

const int N = 5005, mod = 1e9 + 7;
int f[N][N];

int main()
{
	int n, m;
	cin >> n >> m;
	
	for (int i = 1; i <= n; i++) f[i][1] = m;

	for (int i = 2; i <= n; i++)
		for (int j = 2; j <= m; j++)
		{
			f[i][j] = (1ll * f[i - 1][j - 1] * (m - j + 1) + f[i][j]) % mod;
			f[i][j] = (1ll * f[i - 1][j] * j + f[i][j]) % mod;
		}

	cout << f[n][m] % mod;

	return 0;
}