#include<bits/stdc++.h>
#define ll long long
#define int long long
const int nmax = 3e3 + 5, N = 1e6;
const ll oo = 1e9 + 1, base = 311;
const int lg = 19, M = 10;
const ll mod = 1e9 + 7, mod2 = 1e9 + 5277;
#define pii pair<int, int>
#define fi first
#define se second
#define endl "\n"
#define debug(a, n) for(int i = 1; i <= n; ++i) cout << a[i] << ' '; cout << "\n";
using namespace std;
int n, m, dp[nmax][nmax];
ll mul(ll a, ll b){
return a * b % mod;
}
ll calc(int n, int m){
if(n == 0 || m == 0) return 1;
if(n < 0 || m < 0) return 0;
if(dp[n][m] != -1) return dp[n][m];
ll &res = dp[n][m];
res = calc(n - 1, m);
if(m >= 2){
res += mul(calc(n - 1, m - 2), 1ll * m * (m - 1) / 2);
res %= mod;
}
if(n >= 2){
res += mul(calc(n - 2, m - 1), 1ll * (n - 1) * m);
res %= mod;
}
res += mul(calc(n - 1, m - 1) * 4, m);
res %= mod;
return res;
}
main(){
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
// freopen("code.inp", "r", stdin);
// freopen("code.out", "w", stdout);
cin >> n >> m;
memset(dp, -1, sizeof dp);
cout << calc(n, m) - 1;
}
/*
3 1
*/
