import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Collections;

public class Main {

    public static void main(String[] args) throws Exception {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        int max = Integer.parseInt(br.readLine());
        int nums = Integer.parseInt(br.readLine());
        String params[] = br.readLine().split(" ");

        ArrayList<Integer> list = new ArrayList();

        for (int i = 0; i < nums; i++) {
            list.add(Integer.parseInt(params[i]));
        }

        Collections.sort(list);

        int min = max;

        for (int i = list.size() - 1; i >= 0; i--) {
            int tmpNum = max;
            int tmpCount = 0;

            for (int j = i; j >= 0; j--) {
                while (true) {
                    if (tmpNum >= list.get(j)) {
                        tmpNum = tmpNum - list.get(j);
                        tmpCount++;
                    } else {
                        break;
                    }
                }
            }

            if (tmpNum == 0 && min > tmpCount) {
                min = tmpCount;
            }
        }
        if (min != max) {
            System.out.println(min);
            return;
        }

        System.out.println(-1);
    }
}