#include <cassert>
#include <functional>
#include <set>
#include <ctime>
#include <cmath>
#include <climits>
#include <cstring>
#include <string>
#include <queue>
#include <map>
#include <vector>
#include <algorithm>
#include <iostream>
#include <cstdio>
#ifndef ONLINE_JUDGE //POJ
# include <complex>
# include <random>
# include <array>
# define mkt make_tuple
# define empb emplace_back
#endif
#ifdef _LOCAL
# include "for_local.h"
#else
# define debug if (false)
#endif
using namespace std;
typedef unsigned int uint; typedef long long ll; typedef unsigned long long ull;
#define repi(_I, _B, _E) for(int _I = (_B); (_I) < (_E); ++ (_I))
#define rep(_I, _N) for(int _I = 0; (_I) < (_N); ++ (_I))
#define mkp make_pair
#define all(_X) (_X).begin(), (_X).end()

vector<int> as;
int c;
int n;

static int const C_MAX = 100003, N_MAX = 100;
array<int, C_MAX> dp;

int const INF = 1<<29;

signed main()
{
	fill(all(dp), INF);
	dp[0] = 0;

	cin >> c >> n;
	rep(i, n)
	{
		int a;
		cin >> a;
		as.push_back(a);
	}

	rep(ci, c)
	{
		rep(ni, n)
		{
			int const c2 = ci + as[ni];
			if ( c2 > C_MAX ) continue;

			dp[c2] = min(dp[c2], dp[ci] + 1);
		}
	}

	if ( dp[c] == INF ) dp[c] = -1;
	cout << dp[c] << endl;

	return 0;
}