#include <iostream>
#include <string>
#define MOD 1000000007
using namespace std;

int main() {
    long long A; cin >> A;
    string B; cin >> B;
    long long N = B.size();
    
    long long count = 0;
    long long A_pow[N + 1];
    A_pow[1] = A;
    for (long long i = 2; i < N + 1; i++) A_pow[i] = (A_pow[i - 1] * A) % MOD;
    for (long long i = 1; i < N - 1; i++){
        count += (A_pow[i + 1] - A_pow[i]) * i; count %= MOD;
    }
    
    long long dp[N][2];
    for (int i = 0; i < N; i++) dp[i][0] = dp[i][1] = 0;
    for (long long i = 0; i < N; i++){
        if (i == 0){
            dp[i][0] = 1;
            dp[i][1] = B[i] - '0' - 1;
            continue;
        }
        dp[i][0] = dp[i - 1][0];
        dp[i][1] = (dp[i - 1][1] * A + dp[i - 1][0] * (B[i] - '0')) % MOD;
    }
    
    cout << (count + (dp[N - 1][0] + dp[N - 1][1]) * (N - 1)) % MOD << endl;
}