#include <iostream>
#include <string>
#define int long long
using namespace std;

int powmod(int a, int n, int mod) {
	if (n == 0) return 1;
	if (n % 2 == 0) return powmod((a * a) % mod, n / 2, mod);
	return a * powmod(a, n - 1, mod) % mod;
}

int mod = 1000000007;
int a;
string b;

signed main() {
	cin >> a >> b;
	int len = b.length();
	
	int ans = 0;
	for (int n = 0; n < len - 1; n++) {
		int cnt = (powmod(a, n + 1, mod) - powmod(a, n, mod) + mod) % mod;
		//cout << "cnt = " << cnt << endl;
		ans += n * cnt;
		ans %= mod;
	}
	
	int bmod = 0;
	for (int i = 0; i < len; i++) {
		bmod *= a;
		bmod += b[i] - '0';
		bmod %= mod;
	}
	
	int cnt = (bmod + 1 - powmod(a, len - 1, mod) + mod) % mod;
	//cout << "cnt = " << cnt << endl;
	ans += (len - 1) * cnt;
	ans %= mod;
	
	cout << ans << endl;
	return 0;
}