/* -*- coding: utf-8 -*-
 *
 * 247.cc: No.247 線形計画問題もどき - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_C = 100000;
const int MAX_N = 100;

const int INF = 1 << 30;

/* typedef */

/* global variables */

int as[MAX_N];
int dp[MAX_C + 1];

/* subroutines */

/* main */

int main() {
  int c, n;
  cin >> c >> n;

  for (int i = 0; i < n; i++) cin >> as[i];

  dp[0] = 0;

  for (int i = 1; i <= c; i++) {
    int mind = INF;
    for (int j = 0; j < n; j++)
      if (i >= as[j]) {
	int d = dp[i - as[j]] + 1;
	if (mind > d) mind = d;
      }
    dp[i] = mind;
  }

  printf("%d\n", (dp[c] >= INF) ? -1 : dp[c]);
  return 0;
}