import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int c = Integer.parseInt(br.readLine());
        int n = Integer.parseInt(br.readLine());
        int[] values = new int[n];
        String[] line = br.readLine().split(" ", n);
        for (int i = 0; i < n; i++) {
            values[i] = Integer.parseInt(line[i]);
        }
        Arrays.sort(values);
        int[] maxes = new int[c + 1];
        Arrays.fill(maxes, Integer.MAX_VALUE);
        TreeSet<Integer> next = new TreeSet<>();
        next.add(0);
        maxes[0] = 0;
        while (next.size() > 0) {
            int i = next.pollFirst();
            for (int j = 0; j < n && i + values[j] <= c; j++) {
                maxes[i + values[j]] = Math.min(maxes[i + values[j]], maxes[i] + 1);
                next.add(i + values[j]);
            }
        }
        if (maxes[c] == Integer.MAX_VALUE) {
            System.out.println(-1);
        } else {
            System.out.println(maxes[c]);
        }
   }
}