#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2")//,bmi,bmi2,lzcnt,popcnt
#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<ll, ll>;
using piii = pair<ll, pii>;
#define pb push_back
#define F first
#define S second
#define len(x) (int)x.size()
#define all(x) x.begin(),x.end()
#define file freopen("connect.in", "r", stdin);freopen("connect.out", "w", stdout);
#define kill(x) {cout << x << '\n'; continue;}
#define int long long
const int maxn = 3e3 + 5, maxm = 2e5, LG = 20, MOD = 1e9+7;// 998244353
const ll inf = 6e18;
//priority_queue< int, vector<int>, greater<int>> pq; min heap
//priority_queue< int, vector<int>, less<int> > pq; max heap
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
int h, w, dp[maxn][maxn];
signed main() {
ios::sync_with_stdio(0), cin.tie(0);
cin >> h >> w;
for(int i = 0; i <= h; ++i) dp[i][0] = 1;
for(int i = 0; i <= w; ++i) dp[0][i] = 1;
dp[1][1] = 5;
for(int i = 2; i <= max(h, w); ++i) {
dp[1][i] = 4 + i-1 + dp[1][i-1];
dp[1][i] %= MOD;
dp[i][1] = dp[1][i];
}
for(int i = 2; i <= h; ++i)
for(int j = 2; j <= w; ++j) {
dp[i][j] = (4 * j * dp[i-1][j-1] % MOD);
dp[i][j] += ((j*(j-1)/2 % MOD) * dp[i-1][j-2] % MOD) % MOD;
dp[i][j] += ((j*(i-1) % MOD) * dp[i-2][j-1] % MOD) % MOD;
dp[i][j] += dp[i-1][j];
dp[i][j] %= MOD;
}
cout << dp[h][w] - 1;
}
// it was fun while it lasted
// ctrl + d
