typedef long long ll;
typedef long double ld;
#include <bits/stdc++.h>
using namespace std;
#define int long long

const ll MOD = 1e9+7;
long long modpow(long long a, long long n) {
    long long res = 1;
    while (n > 0) {
        if (n & 1) res = res * a % MOD;
        a = a * a % MOD;
        n >>= 1;
    }
    return res;
}

signed main(){
    ll a;
    std::cin >> a;
    string b;
    std::cin >> b;
    reverse(b.begin(),b.end());
    ll n = b.size();
    ll ans = 0;
    ll bv = 0;
    for (int i = 0; i < n; i++) {
        if(i!=n-1){
            ans += (modpow(a, i+1)-modpow(a,i)+MOD)%MOD*i%MOD;
            ans %= MOD;
            bv += modpow(a, i)*(b[i]-'0')%MOD;
            bv %= MOD;
        }else{
            bv += modpow(a, i)*(b[i]-'1')%MOD;
            ans += (bv+1)*i;
            ans %= MOD;
        }
    }
    std::cout << ans << std::endl;
}