#include<iostream>
#define maxn 1000
using namespace std;
typedef long long ll;
int n,m;
ll ans=0,EDG=1e9+7;
int main()
{
	cin>>n>>m;
	for(int i=1;i<=n;i++)
	{
		ll temp=i;
		ans=(ans+temp)%EDG;
		for(int j=1;j<m;j++)
	    {
		    temp=temp*i%EDG;
		    ans=(ans+temp)%EDG;
		    ///cout<<"ans="<<ans<<endl;
    	}
	}
	cout<<ans<<endl;
	return 0;
}