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#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,b) for (int i = (a); i <= (b); ++i)
#define REPD(i,a,b) for (int i = (a); i >= (b); --i)
#define FORI(i,n) REP(i,1,n)
#define FOR(i,n) REP(i,0,int(n)-1)
#define mp make_pair
#define pb push_back
#define pii pair<int,int>
#define vi vector<int>
#define ll long long
#define SZ(x) int((x).size())
#define DBG(v) cerr << #v << " = " << (v) << endl;
#define FOREACH(i,t) for (typeof(t.begin()) i=t.begin(); i!=t.end(); i++)
#define fi first
#define se second

const int N = 3030;
const int mod = 1000000007;

int n,m;
int dop[N], dcl[N];

int main() {
	scanf("%d%d", &n, &m);
	dop[0] = 1;
	int res = 0;
	for (int k = 1; k <= n && k <= m; k++) {
		for (int i = 1; i <= n; i++) {
			dcl[i] = (1LL * (m-k) * dcl[i-1] + 1LL * (m-k+1) * dop[i-1]) % mod;
		}
		dop[0] = 0;
		for (int i = 1; i <= n; i++) {
			dop[i] = (1LL * k * dcl[i-1] + 1LL * k * dop[i-1]) % mod;
		}
		res = (res + dop[n]) % mod;
	}
	
	printf("%d\n", res);
	return 0;
}