#include <bits/stdc++.h>
#define F first
#define S second
#define all(a) begin(a), end(a)
#define pb push_back
#define eb emplace_back
using namespace std;
using ll = long long;
int const MOD = 1e9 + 7;
int const N = 3009;
int inv2 = (MOD + 1) / 2;
int add(ll a, ll b) {
ll ret = (a + b) % MOD;
if (ret < 0) ret += MOD;
return ret;
}
int mul(ll a, ll b) {
ll ret = (a * b) % MOD;
if (ret < 0) ret += MOD;
return ret;
}
int memo[N][N];
int f(int n, int m) {
if (n == 0 || m == 0) return 1;
/*if (min(n, m) == 1) {
if (m == 1) swap(n, m);
int mC2 = mul(mul(m, m - 1), inv2);
return add(mul(4, m), mC2);
}*/
if (memo[n][m] != -1) return memo[n][m];
int mC2 = mul(mul(m, m - 1), inv2);
memo[n][m] = 0;
memo[n][m] = add(memo[n][m], f(n-1, m));
memo[n][m] = add(memo[n][m], mul(mul(4, m), f(n - 1, m - 1)));
if (m >= 2) memo[n][m] = add(memo[n][m], mul(mC2, f(n - 1, m - 2)));
if (n >= 2) memo[n][m] = add(memo[n][m], mul(mul(m, n - 1), f(n - 2, m - 1)));
return memo[n][m];
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
for (auto &arr : memo)
memset(arr, -1, sizeof arr);
int H, W;
cin >> H >> W;
cout << add(f(H, W), -1) << '\n';
return 0;
}
