#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <numeric>
#include <bitset>
#include <complex>
#define rep(x, to) for (int x = 0; x < (to); x++)
#define REP(x, a, to) for (int x = (a); x < (to); x++)
#define foreach(itr, x) for (typeof((x).begin()) itr = (x).begin(); itr != (x).end(); itr++)
#define EPS (1e-14)
#define INF (1e+9)

using namespace std;

typedef long long ll;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;
typedef complex<double> Complex;
typedef vector< vector<int> > Mat;

int C;
int N;
int a[100005];
int dp[105][100005];

int main() {
	rep(i, 105) rep(j, 100005) dp[i][j] = INF;
	cin >> C;
	cin >> N;
	rep(i, N) cin >> a[i];
	dp[0][0] = 0;
	for (int i = 0; i < N; i++) {
		for (int j = 0; j <= C; j++) {
			dp[i + 1][j] = dp[i][j];
			if (j - a[i] >= 0) {
				dp[i + 1][j] = min(dp[i + 1][j], dp[i + 1][j - a[i]] + 1);
			}
		}
	}
	if (dp[N][C] == INF) {
		cout << -1 << endl;
	} else {
		cout << dp[N][C] << endl;
	}
	return 0;
}