#include <iostream>
using namespace std;
#define rep(i, a, b) for (ll i = (a); i <= (b); ++i)
using ll = long long;
const int N = 3 << 10, M = 1e9 + 7;
ll dp[N][N];
signed main() {
int h, w; cin >> h >> w;
rep(i, 0, h) dp[i][0] = 1;
rep(j, 0, w) dp[0][j] = 1;
rep(i, 1, h) {
rep(j, 1, w) {
auto add = [&](ll x) {
dp[i][j] += x;
if (M <= dp[i][j]) dp[i][j] -= M;
};
if (i != 1) add(i * (i - 1) / 2 % M * dp[i - 2][j - 1] % M);
add(4 * i * dp[i - 1][j - 1] % M);
add(dp[i][j - 1]);
if (j != 1) add(i * (j - 1) % M * dp[i - 1][j - 2] % M);
}
}
cout << (dp[h][w] + M - 1) % M;
}
