package main;
import java.util.*;
public class Main {

    public static final int INF = 1 << 29;
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int c = sc.nextInt();
        int n = sc.nextInt();
        int[] a = new int[n];
        
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        
        int[] dp = new int[c + 1];
        
        Arrays.fill(dp, INF);
        dp[0] = 0;
        
        for (int i = 0; i < n; i++) {
            for (int j = 0; j <= c; j++) {
                if (j >= a[i]) {
                    dp[j] = Math.min(dp[j], dp[j - a[i]] + 1);
                }
            }
        }
        
        System.out.println(dp[c] == INF ? -1 : dp[c]);
    }

}