#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <set>
#include <map>
#include <limits>
#include <unordered_map>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

typedef long long ll;
typedef unsigned long long ull;

int N, C;
int A[101];

int constexpr INF = 1e6;
int constexpr MAX = 1e7+1;

int dp[MAX];

int main() {

  cin >> C >> N;
  rep(i, N) cin >> A[i];

  rep(i, C+1) dp[i] = INF;
  dp[0] = 0;

  rep(i, N)
    rep(j, C+1)
      if(j - A[i] >= 0 && dp[j - A[i]] < INF)
        dp[j] = min(dp[j], dp[j - A[i]] + 1);

  cout << (dp[C] == INF ? -1 : dp[C]) << endl;

  return 0;
}