#include <bits/stdc++.h>
#include <atcoder/modint>
using mint = atcoder::modint1000000007;
using namespace std;
using ll = long long;

int main() {
    int a;
    string b;
    cin >> a >> b;

    reverse(b.begin(), b.end());
    int n = b.size();
    for (int i = 0; i < n; i++) {
        b[i] -= '0';
    }

    mint c = 1, t = 1, r = 0;
    for (int i = 0; i < n; i++) {
        c += t * (i == n - 1 ? b[i] - 1 : b[i]);
        if (i < n - 1) r += t * (a - 1) * i;
        t *= a;
    }
    r += c * (n - 1);

    cout << r.val() << endl;

    return 0;
}