#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <algorithm>
#include <cmath>
#include <string>

using namespace std;

typedef vector <int> VI;
typedef vector <VI> VVI;
typedef vector <string> VS;
typedef pair<int,int> PII;
typedef long long LL;
typedef unsigned long long ULL;
typedef pair <int, LL> PIL;
typedef vector <PIL> VPIL;

#define each(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); i++)
#define sort(c) sort((c).begin(),(c).end())

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

#define MAX_INT 2147483647

int main(){
	int C, N, UB = 100001;
	VI a;
	VVI dp;
	cin >> C >> N;
	a.resize(N);
	rep(i,N) cin >> a[i];
	dp = VVI(N+1, VI(C+1, UB));
	rep(i,N){
		dp[i][0] = 0;
		range(j,a[i],C+1) dp[i][j] = min(dp[i][j], dp[i][j-a[i]]+1);
		rep(j,C+1) dp[i+1][j] = dp[i][j]; 
	}
  	cout << ((dp[N][C] != UB)? dp[N][C] : -1) << endl;
	return 0;
}