#include<iostream>
#include<vector>
#include<list>
typedef long long ll;

using namespace std;
const ll p=(ll) 1e9+7;

ll powmod(ll a, ll n) {
		return n!=0?powmod(a*a%p,n/2)*(n%2==1?a:1)%p:1;
}

ll tolong(string B, ll A) {
		ll x=0;
		for (int i=0;i<B.size();++i) {
				x=x*A%p;
				x+=B[i]-'0';
		}
		return x;
}

int main() {
		long long x = 0;
		int A;
		string B;
		cin >> A;
		cin >> B;
		int n=B.size();
		ll upper=(tolong(B,A)+1)%p;
		for (int i=1;i<=n;++i) {
				x+= ((i==n?upper:powmod(A, i)) - powmod(A, i-1) + p) * (i-1) % p;
				x%=p;
		}
		cout << x << endl;
}