#include <algorithm>
#include <vector>
#include <cfloat>
#include <string>
#include <cmath>
#include <set>
#include <cstdlib>
#include <map>
#include <ctime>
#include <iomanip>
#include <functional>
#include <deque>
#include <iostream>
#include <cstring>
#include <queue>
#include <cstdio>
#include <stack>
#include <climits>
#include <sys/time.h>
#include <cctype>

using namespace std;

typedef long long ll;

int main() {
  int c;
  scanf("%d", &c);
  int n;
  scanf("%d", &n);
  int a[n];
  for (int i = 0; i < n; i++) {
    scanf("%d", &a[i]);
  }

  int dp[c+1];
  memset(dp, -1, sizeof(dp));
  dp[0] = 0;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < c; j++) {
      if (dp[j] != -1 && j+a[i] <= c) {
	if (dp[j+a[i]] == -1) {
	  dp[j+a[i]] = dp[j]+1;
	}else {
	  dp[j+a[i]] = min(dp[j+a[i]], dp[j]+1);
	}
      }
    }
  }

  printf("%d\n", dp[c]);
}