#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

#include <atcoder/modint>
using mint = atcoder::modint1000000007;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int a;
  string b;
  cin >> a >> b;
  reverse(b.begin(), b.end());
  mint ans = 0;
  rep(i, b.size()) {
    if (i == b.size() - 1) {
      mint bb = 0;
      rep(i, b.size()) bb += (b[i] - '0') * mint(a).pow(i);
      ans += i * (bb - mint(a).pow(i) + 1);
    }
    else
      ans += i * (a - 1) * mint(a).pow(i);
  }
  cout << ans.val() << '\n';
  return 0;
}