#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

//INSERT ABOVE HERE
signed main(){
  Int c,n;
  cin>>c>>n;
  vector<Int> a(n);
  for(Int i=0;i<n;i++) cin>>a[i];
  
  const Int MAX = 2.1e5;
  const Int INF = 1e15;
  vector<Int> dp(MAX,INF);
  dp[0]=0;
  for(Int i=0;i<n;i++)
    for(Int j=0;j+a[i]<MAX;j++)
      chmin(dp[j+a[i]],dp[j]+1);

  Int ans=dp[c]>=INF?-1:dp[c];
  cout<<ans<<endl;
  return 0;
}