#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cmath>
#include <stdio.h>
#include <queue>
#include <deque>
#include <cstdio>
#include <set>
#include <map>
#include <bitset>
#include <stack>
#include <cctype>
using namespace std;
long long mod = 1000000007;
long long m_pow(long long x, long long y) {
	long long ans = 1;
	while (y > 0) {
		if ((y & 1) == 1) {
			ans = ans * x % mod;
		}
		x = x * x % mod;
		y >>= 1;
	}
	return ans;
}
int main() {
	long long a;
	string b;
	cin >> a >> b;
	long long ans = 0, num = 0, a1 = 1, n = b.size();
	for (int i = n - 1; i >= 0; i--) {
		num += a1 * (b[i] - '0');
		num %= mod;
		a1 *= a;
		a1 %= mod;
	}
	for (long long i = 0; i < n - 1; i++) {
		ans += i * (m_pow(a, i + 1) - m_pow(a, i));
		ans %= mod;
	}
	ans += (n - 1) * (num - m_pow(a, n - 1) + 1);
	ans %= mod;
	cout << (ans + mod) % mod << endl;
}