#include<stdio.h>
#define P 1000000007
int fast(int a,int b){
    int res=1;
    while(b){
        if(b&1)res=1LL*res*a%P;
        b>>=1;
        a=1LL*a*a%P;
    }
    return res;
}
int main(){
//  freopen("sum.in","r",stdin);
//  freopen("sum.out","w",stdout);
    int n,m,ans=0;
    scanf("%d %d",&n,&m);
    for(int i=1;i<=n;i++){
        if(i==1)ans+=m;
        int x=1LL*i*(fast(i,m)-1+P)%P;
        ans=(ans+1LL*x*fast(i-1,P-2))%P;
    }
    printf("%d\n",ans%P);
    return 0;
}