import java.util.*;

class Main {
	static int INF = 2 << 27;
	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(dp[j] == INF) {
					continue;
				}
				if(j + a[i] > c) {
					break;
				}
				
				dp[j + a[i]] = Math.min((dp[j] + 1),dp[j + a[i]]);
			}
		}
		int min = dp[c];
		if(min == INF) {
			min = -1;
		}
		System.out.println(min);
		
		
		
		
	}
}