#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1000000007;
int main(){
  int A;
  cin >> A;
  string B;
  cin >> B;
  int N = B.size();
  vector<long long> POW(N);
  POW[0] = 1;
  for (int i = 0; i < N - 1; i++){
    POW[i + 1] = POW[i] * A % MOD;
  }
  long long x = 0;
  for (int i = 0; i < N; i++){
    x = (x * A + (B[i] - '0')) % MOD;
  }
  long long ans = x * (N - 1) % MOD;
  for (int i = 1; i < N; i++){
    ans += MOD - POW[i] + 1;
    ans %= MOD;
  }
  cout << ans << endl;
}