#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;
int dp[100010];
int a[100010];
int main(){
	int c, n;
	cin >> c >> n;
	dp[0] = 0;
	for (int i = 1; i <= c; i++) {
		dp[i] = 1000000007;
	}
	for (int i = 0; i < n; i++) {
		cin >> a[i];
		for (int j = a[i]; j <= c; j++) {
			dp[j] = min(dp[j], dp[j - a[i]] + 1);
		}
	}
	if (dp[c] == 1000000007)cout << -1 << endl;
	else cout << dp[c] << endl;
}