#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
const int md = 1e9 + 7;
void add(int &a, int b) {
a += b;
if (a >= md) a -= md;
if (a < 0) a += md;
}
int mul(int a, int b) {
return ((ll)a * b) % md;
}
int power(int a, ll b) {
int res = 1;
while (b > 0) {
if (b & 1) res = mul(res, a);
a = mul(a, a);
b >>= 1;
}
return res;
}
int inv(int a) {
return power(a, md - 2);
}
const int N = 3007;
int C[N][N];
int f[N], rf[N];
int main() {
ios_base::sync_with_stdio(false); cin.tie(0); cout.setf(ios::fixed); cout.precision(20);
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
f[0] = 1;
for (int i = 1; i < N; ++i) f[i] = mul(f[i - 1], i);
for (int i = 0; i < N; ++i) rf[i] = inv(f[i]);
int n, m;
cin >> n >> m;
vector <vector <int>> dp(n + 1, vector <int> (m + 1));
C[0][0] = 1;
for (int n = 1; n < N; ++n) {
C[n][0] = 1;
for (int k = 1; k < N; ++k) {
add(C[n][k], C[n - 1][k]);
add(C[n][k], C[n - 1][k - 1]);
}
}
for (int i = 0; i <= n; ++i) dp[i][0] = 1;
for (int j = 0; j <= m; ++j) dp[0][j] = 1;
for (int i = 1; i <= n; ++i) {
for (int j = 1; j <= m; ++j) {
add(dp[i][j], dp[i - 1][j]);
if (j >= 2) add(dp[i][j], mul(C[j][2], dp[i - 1][j - 2]));
if (i >= 2) add(dp[i][j], mul(j, mul(i - 1, dp[i - 2][j - 1])));
}
}
int ans = 0;
int st = 1;
int cur = 1;
for (int cnt = 0; cnt <= min(n, m); ++cnt) {
add(ans, mul(mul(cur, mul(st, dp[n - cnt][m - cnt])), rf[cnt]));
st = mul(st, 4);
cur = mul(cur, n - cnt);
cur = mul(cur, m - cnt);
}
add(ans, -1);
cout << ans << '\n';
}
