#include <iostream>
#include <algorithm>
using namespace std;

int main(void) {
  constexpr int inf = 987654321;
  int c, n; scanf("%d%d", &c, &n);
  vector<int> a(n, 0);
  for(int i=0; i<n; ++i) { scanf("%d", &a[i]); }
  vector<int> dp(c+1, inf);
  dp[0] = 0;
  for(int i=0; i<n; ++i) {
    for(int acc=0; acc+a[i]<=c; ++acc) {
      dp[acc+a[i]] = min(dp[acc+a[i]], dp[acc] + 1);
    }
  }
  int res = dp[c];
  if(res == inf) { res = -1; }
  printf("%d\n", res);
  return 0;
}