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

typedef long long ll;
typedef pair< int, int > pii;
typedef vector< int > vi;
typedef vector< vi > vvi;
typedef vector< ll > vl;
typedef vector< vl > vvl;
typedef vector< pii > vp;
typedef vector< vp > vvp;
typedef vector< string > vs;
typedef vector< double > vd;
typedef vector< vd > vvd;

template< class T1, class T2 >
int upmin( T1 &x, T2 v ){
  if( x > v ){
    x = v;
    return 1;
  }
  return 0;
}

template< class T1, class T2 >
int upmax( T1 &x, T2 v ){
  if( x < v ){
    x = v;
    return 1;
  }
  return 0;
}

const int INF = 0x3f3f3f3f;

int C;
int N;
vi A;

void init(){
  cin >> C;
  cin >> N;
  A = vi( N );
  for( int i = 0; i < N; ++i )
    cin >> A[ i ];
}

vi dp;

void preprocess(){
  dp = vi( C + 1, INF );
  dp[ 0 ] = 0;
  for( int i = 0; i < N; ++i )
    for( int j = 0; j <= C; ++j ){
      if( j + A[ i ] <= C )
        upmin( dp[ j + A[ i ] ], dp[ j ] + 1 );
    }
}

void solve(){
  if( dp[ C ] < INF )
    cout << dp[ C ] << endl;
  else
    cout << -1 << endl;
}

signed main(){
  ios::sync_with_stdio( 0 );
  init();
  preprocess();
  solve();
  return 0;
}