#include <bits/stdc++.h>

using namespace std;

int dp[100001];

int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);
	
	int c, n, t;
	vector <int> v;

	cin >> c;
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> t;
		v.push_back(t);
	}

	sort(v.rbegin(), v.rend());

	fill(dp, dp + 100001, 1e9);

	dp[c] = 0;

	for (int i = 0; i < n; i++)
	{
		for (int j = c; j >= 0; j--)
		{
			if (dp[j] >= 1e9) continue;
			int x = j / v[i];
			int y = j % v[i];
			dp[y] = min(dp[y], dp[j] + x);
		}
	}

	if (dp[0] >= 1e9)
	{
		dp[0] = -1;
	}

	cout << dp[0] << '\n';

	return 0;
}