#include<bits/stdc++.h>
using namespace std;
#define int long long

const int MOD = 1e9+7;
const int INF = 1LL << 60;

int dp[101][101010];

signed main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  int C,N; cin >> C >> N;
  vector<int> a(N);
  for(int i = 0; i < N; i++){
    cin >> a[i];
  }

  fill(dp[0],dp[100]+101010,INF);
  dp[0][0] = 0;
  for(int i = 0; i < N; i++){
    for(int j = 0; j <= C; j++){
      if(j-a[i] >= 0){
        dp[i+1][j] = min(dp[i][j],dp[i+1][j-a[i]]+1);
      }
      else dp[i+1][j] = dp[i][j];
    }
  }
  if(dp[N][C] == INF) cout << -1 << endl;
  else cout << dp[N][C] << endl;

  return 0;
}