#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <fstream>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int v, w; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

int main() {
	int C, N; cin >> C >> N;
	vector<int> a(N);
	for (int i = 0; i < N; i++)
		cin >> a[i];
	vector<ll> dp(C + 1, INT_MAX);
	dp[0] = 0;
	for (int i = 0; i < N; i++)
		for (int j = 0; j + a[i] <= C; j++)
			dp[j + a[i]] = min(dp[j + a[i]], dp[j] + 1);
	if (dp[C] == INT_MAX) dp[C] = -1;
	cout << dp[C] << endl;
}