#include <bits/stdc++.h>
#include <atcoder/all>

using std::cin;
using std::cout;
using namespace atcoder;
using mint = modint1000000007;
using std::string;
using ll = long long;

int main() {
	int a;
	string b;
	cin >> a >> b;
	int n = b.size();
	reverse(b.begin(), b.end());
	
	mint ans, mul = 1, t;
	for (int i = 0; i < n; ++i) {
		ans -= mul - 1;
		t += mint(b[i] - '0') * mul;
		mul *= a;
	}
	
	ans += t * (n - 1);
	
	cout << ans.val() << '\n';
	
	return 0;
}