#include<iostream>
using namespace std;
#define MOD 1000000007
typedef long long int lld;
lld DP[6000][6000];
lld trabalha(int x, int y){
if(x<0 || y<0)return 0;
if(DP[x][y]!=-1)return DP[x][y];
lld ans=0;
ans+=trabalha(x-1,y);
ans%=MOD;
ans+=4*y*trabalha(x-1,y-1);
ans%=MOD;
lld comb=y*(y-1);
comb/=2;
comb%=MOD;
//cout<<ans<<endl;
ans+=comb*trabalha(x-1,y-2);
comb=y*(x-1);
comb%=MOD;
//cout<<ans<<endl;
ans+=comb*trabalha(x-2,y-1);
ans%=MOD;
DP[x][y]=ans;
return ans;
}
int main(){
for(int i=0;i<6000;i++){
for(int j=0;j<6000;j++){
DP[i][j]=-1;
if(i==0 || j==0)DP[i][j]=1;
}
}
int x,y;
cin>>x>>y;
cout<<(trabalha(x,y)+MOD-1)%MOD<<endl;
/*for(int i=0;i<=x;i++){
for(int j=0;j<=y;j++){
cout<<i<<" "<<j<<" "<<DP[i][j]<<endl;
}
}*/
return 0;
}
