#include<bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using mint=modint1000000007;
using ll=long long;
using pp=pair<int,int>;
#define sr string 
#define vc vector
#define fi first
#define se second
#define rep(i,n) for(int i=0;i<(int)n;i++)
#define pb push_back
#define all(v) v.begin(),v.end()
#define pque priority_queue
#define bpc(a) __builtin_popcount(a)
int main(){
  int a;sr s;cin>>a>>s;
  int n=s.size();
  mint x=0;
  reverse(all(s));
  mint t=1;
  mint ans=0;
  for(auto c:s){
    int cx=c-'0';
    x+=t*cx;
    t*=a;
  }
  t/=a; t--;
  ans+=(x-t)*(n-1);
  rep(i,n-1)ans+=mint(a).pow(i)*(a-1)*i;
  cout<<ans.val();
}