#include<bits/stdc++.h>
#define int long long
using namespace std;
constexpr int mod=1000000007;
signed main(){
  int A;
  string B;
  cin>>A>>B;
  int N=B.size();
  int ans=0;
  int p=1;
  for(int i=0;i<N-1;i++,(p*=A)%=mod){
    (ans+=i*(p*(A-1)%mod))%=mod;
  }
  int m=0;
  for(char c:B){
    ((m*=A)+=c-'0')%=mod;
  }
  m=(m-p+1+mod)%mod;
  cout<<(ans+m*(N-1)%mod)%mod<<endl;
}