#include <iostream>
#include <string>
using namespace std;
using ll = long long;
using ull = unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)


const ull MOD = 1000000007;

int main(){
  int A;
  string S;
  cin >> A >> S;
  ull ans = 0;
  ull cnt = 0;
  for(char c : S){
    cnt = cnt * A + (c - '0');
    cnt %= MOD;
  }
  ans += cnt * (S.size() - 1) % MOD;
  ull tmp = 0;
  for(char c : S.substr(1)){
    tmp = tmp * A + (A-1);
    tmp %= MOD;
    ans += MOD - tmp;
    ans %= MOD;
  }
  cout << ans << endl;
  return 0;
}

struct ios_do_not_sync{
  ios_do_not_sync(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
  }
} ios_do_not_sync_inst;