package no247;

import java.util.Arrays;
import java.util.Scanner;

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[n+1][c+1];
		for(int i=0;i<=n;i++) {
			Arrays.fill(dp[i], INF);
		}
		for(int i=0;i<=n;i++) {
			dp[i][0] = 0;
		}
		for(int i=1;i<=n;i++) {
			for(int j=0;j<=c;j++) {
				dp[i][j] = dp[i-1][j];
				if (j >= a[i-1]) {
					dp[i][j] = Math.min(dp[i][j], dp[i][j-a[i-1]] + 1);
				}
			}
		}
		System.out.println(dp[n][c] == INF ? -1 : dp[n][c]);
	}

}