#include <iostream>
#include <vector>
#include <climits>
int dp(const std::vector<int> &series, const int &c) {
	std::vector<int> res(c + 1, INT_MAX);
	res.at(0) = 0;
	for (const auto &a : series) {
		for (auto i = 0; i <= c - a; ++i) {
			if (res.at(i) < INT_MAX && res.at(i + a) > res.at(i) + 1) {
				res.at(i + a) = res.at(i) + 1;
			}
		}
	}
	return res.at(c);
}
int main() {
	int c, n;
	std::cin >> c >> n;
	std::vector<int> series(n);
	for (auto &a : series) {
		std::cin >> a;
	}
	auto res = dp(series, c);
	if (res == INT_MAX) {
		std::cout << -1 << std::endl;
	}
	else {
		std::cout << res << std::endl;
	}
	return 0;
}