#include <iostream>
#define MOD 1000000007
using namespace std;
long long dp_ind[3001][3001];
long long dp_ttl[3001][3001];
int main () {
int n, m;
cin >> n >> m;
for (int i=1; i<=n; i++) {
for (int j=1; j<=m; j++) {
dp_ind[i][j] = (4ll*(dp_ttl[i-1][j-1]+1))%MOD;
dp_ind[i][j] += (1ll*(dp_ttl[max(0, i-2)][j-1]+(i>1?1:0))*(i-1)+(dp_ttl[i-1][max(0, j-2)]+(j>1?1:0))*(j-1))%MOD;
dp_ttl[i][j] = (1ll*dp_ttl[i-1][j]+dp_ttl[i][j-1]-dp_ttl[i-1][j-1]+dp_ind[i][j]+MOD)%MOD;
}
}
cout << dp_ttl[n][m] << endl;
}
