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


public class Main_yukicoder247 {

    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();
        }

        final int INF = Integer.MAX_VALUE / 2;
        int[][] dp = new int[n + 1][c + 1];
        for (int i = 0; i <= n; i++) {
        	Arrays.fill(dp[i], INF);
        }
        
        for (int i = 1; i <= n; i++) {
            dp[i][0] = 0;
        	for (int j = 1; j <= c; j++) {
        		dp[i][j] = Math.min(dp[i][j], dp[i - 1][j]);
        		if (j >= a[i - 1]) {
        			dp[i][j] = Math.min(dp[i][j], dp[i - 1][j - a[i - 1]] + 1);
        			dp[i][j] = Math.min(dp[i][j], dp[i][j - a[i - 1]] + 1);
        		}
        	}
        }

        int min = INF;
        for (int i = 1; i <= n; i++) {
        	min = Math.min(min, dp[i][c]);
        }

        if (min == INF) {
        	System.out.println(-1);
        } else {
        	System.out.println(min);
        }

        sc.close();
    }
}