#include <vector>
#include <iostream>
#include <climits>
void sort(std::vector<int> &vector, int left, int right) {
	if (left < right) {
		auto l = left, r = right, pivot = vector.at((left + right) / 2);
		while (l < r) {
			while (vector.at(l) > pivot)++l;
			while (vector.at(r) < pivot)--r;
			if (l < r) {
				auto temp = vector.at(l);
				vector.at(l) = vector.at(r); vector.at(r) = temp;
				++l; --r;
			}
			sort(vector, left, r), sort(vector, r + 1, right);
		}
	}
}
int main() {
	int c, n;
	std::cin >> c >> n;
	std::vector<int> vector(c + 1, INT_MAX);
	std::vector<int> arr(n, 0);
	for (auto &i : arr) {
		int a;
		std::cin >> a;
		i = a;
	}
	sort(arr, 0, arr.size() - 1);
	vector.at(0) = 0;
	int min = INT_MAX;
	for (const auto &a : arr) {
		for (auto i = 0; i < c + 1; ++i) {
			if (vector.at(i) < min && (i + a <= c) && (vector.at(i + a) > vector.at(i) + 1)) {
				vector.at(i + a) = vector.at(i) + 1;
				if ((i + a == c) && (min > vector.at(i + 1))) {
					min = vector.at(i + 1);
				}
			}
		}
	}
	if (vector.at(c) == INT_MAX) {
		std::cout << -1 << std::endl;
	}
	else {
		std::cout << vector.at(c) << std::endl;
	}
	return 0;
}