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

constexpr int MOD = 1e9+7;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int A; string B; cin >> A >> B;
    int N = B.size();
    ll ans = 0, sB = 0, pA = 1;
    for(int i = N - 1; i >= 1; i--) {
        ans += (N - 1 - i) * pA % MOD * (A - 1) % MOD;
        if(ans >= MOD) ans -= MOD;
        sB += (B[i] - '0') * pA % MOD;
        if(sB >= MOD) sB -= MOD;
        pA *= A;
        pA %= MOD;
    }

    // A^i <= x <= B
    // B - A^i + 1
    sB += (B[0] - '0') * pA;
    ans += (N - 1) * (sB - pA + 1) % MOD;
    cout << ans % MOD << "\n";
}