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

public class Main {
    static int[] values;
    static int[][] dp;
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int c = sc.nextInt();
        int n = sc.nextInt();
        int[] values = new int[n];
        for (int i = 0; i < n; i++) {
            values[i] = sc.nextInt();
        }
        int[] dp = new int[c + 1];
        Arrays.fill(dp, Integer.MAX_VALUE);
        dp[0] = 0;
        for (int i = 0; i <= c; i++) {
            for (int j = 0; j < n; j++) {
                if (i >= values[j] && dp[i - values[j]] != Integer.MAX_VALUE) {
                    dp[i] = Math.min(dp[i], dp[i - values[j]] + 1);
                }
            }
        }
        if (dp[c] == Integer.MAX_VALUE) {
            System.out.println(-1);
        } else {
            System.out.println(dp[c]);
        }
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String nextLine() throws Exception {
        return br.readLine();
    }
    
    public String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}