#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <limits.h>
#include <map>
#include <queue>
#include <set>
#include <string.h>
#include <vector>

using namespace std;
typedef long long ll;

int main() {
  int C;
  cin >> C;

  int N;
  cin >> N;

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

  vector<int> dp(C + 1, C + 1);
  dp[0] = 0;
  for (int c = 0; c < C; ++c) {
    for (int i = 0; i < N; ++i) {
      int a = A[i];
      if (a + c > C) continue;

      dp[a + c] = min(dp[a + c], dp[c] + 1);
    }
  }

  if (dp[C] == C + 1) {
    cout << -1 << endl;
  } else {
    cout << dp[C] << endl;
  }

  return 0;
}