#include<bits/stdc++.h>
#define ll long long
#define pii pair<int,int>
using namespace std;
const int mxn=1e5+5;
const int inf=1e9;
const ll mod=1e9+7;
ll nc2(ll n) {
ll res= n * (n-1) /2 % mod;
return res % mod;
}
int main() {
int h,w;
cin>>h>>w;
ll dp[h+1][w+1];
for(int i=1;i<=w;i++) {
dp[1][i] = ( 4 * i + nc2(i) + 1) % mod ;
dp[0][i]=1;
}
for(int i=1;i<=h;i++) {
dp[i][1] = ( 4 * i + nc2(i) + 1) % mod;
dp[i][0]=1;
}
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;
//cout<<dp[i][j]<<endl;
dp[i][j] += nc2(j) * dp[i-1][j-2] % mod;
dp[i][j] %= mod;
//cout<<dp[i][j]<<endl;
dp[i][j] += (j * (i-1) % mod) * dp[i-2][j-1] % mod;
dp[i][j] %= mod;
dp[i][j] = (dp[i][j] + dp[i-1][j]) % mod;
}
}
cout<<(dp[h][w] - 1 + mod) % mod<<endl;
}
