#include <iostream>
using namespace std;
typedef long long ll;

const ll MOD = 1000000007;

int main()
{
    int a;
    string b;
    cin >> a >> b;
    int n = b.size();
    ll s = a - 1;
    ll ans = n - 1;
    for(int i = 0; i < n - 1; i++){
        ans = (ans + i * s) % MOD;
        s = (s * a) % MOD;
    }
    s = 1;
    b[0]--;
    for(int i = n - 1; i >= 0; i--){
        ans = (ans + (n - 1) * s * (b[i] - '0')) % MOD;
        s = s * a % MOD;
    }
    cout << ans << endl;
}