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

int C,N,a[110];
int min_cost[100100];
int main(){
  cin >> C >> N;
  for(int i=1;i<=C;i++){
    min_cost[i] = 1001001001;
  }
  for(int i=0;i<N;i++){
    cin >> a[i];
    min_cost[a[i]] = 1;
  }
  sort(a,a+N);
  for(int i=0;i<N;i++){
    int t=a[i];
    for(int j=1;j<=C;j++){
      if(j-t < 0) continue;
      min_cost[j] = min(min_cost[j],min_cost[j-t] + 1);
    }
  }
  if(min_cost[C] >= 1001001001) cout << "-1" << endl;
  else cout << min_cost[C] << endl;
}