#include <bits/stdc++.h>

using namespace std;

typedef long long LL;

const int N = 3005, P = 1e9 + 7;

int n, m;
LL c[N][N], fact[N * 2], p2[N * 2];

int main()
{
    scanf("%d%d", &n, &m);
    if(n < m) swap(n, m);
    
    for(int i = 0; i <= n; i ++ )
    {
        c[i][0] = 1;
        for(int j = 1; j <= i; j ++ )
            c[i][j] = (c[i - 1][j - 1] + c[i - 1][j]) % P;
    }
    fact[0] = 1;
    for(int i = 1; i <= n * 2; i ++ ) fact[i] = fact[i - 1] * i % P;
    p2[0] = 1;
    for(int i = 1; i <= n * 2; i ++ ) p2[i] = p2[i - 1] * (P + 1) / 2 % P;

    LL res = 0;
    for(int i = 0; i <= m; i ++ )
    {
        LL s = 0;
        for(int j = 0; j <= min(n - i, 2 * m - i - n); j ++ )
        {
            s = (s + (i & 1 ? P - p2[n - m + i + j * 2] : p2[n - m + i + j * 2]) * c[n - i][j] % P * fact[n - i + j] % P * c[m - i][n - m + j]) % P; 
            // printf("#%d %d %lld\n", i, j, c[n][i] % P * c[m][i] % P * c[n - i][j] % P * f[m - i][n - i + j] % P);
        }
        res = (res + s * c[n][i] % P * c[m][i] % P * fact[i]) % P;
    }
    
    printf("%lld\n", res);
    return 0;
}