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#include <cstdio>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;

int Q = (int(1e9)) + 7;

void add(int& x, int y) {
	x += y;
	if (x > Q) x -= Q;
}

int mn(long long x, int y) {
	return x * y % Q;
}

const int M = 3013;

int d[M][M], z[M][M];

int main() {
	int n, m;
	scanf("%d %d", &n,&m);
	d[0][0] = 1;
	for (int i = 0; i < n; i++)
		for (int w = 0; w <= i && w <= m; w++) {
	//		printf("d[%d][%d]= %d   z = %d\n",i,w,d[i][w],z[i][w]);
			add(d[i+1][w], mn(d[i][w], w));
			add(z[i+1][w+1], mn(d[i][w], m-w));
			
			add(d[i+1][w], mn(z[i][w], w));
			add(z[i+1][w], mn(z[i][w], m-w));
		}
	int s = 0;
	for (int w = 0; w <= n && w <= m; w++) {
//		printf("d[%d][%d]= %d   z = %d\n",n,w,d[n][w],z[n][w]);
		add(s, d[n][w]);
	}
	printf("%d\n", s);
	return 0;
}