#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
//#include<cctype>
#include<climits>
#include<iostream>
#include<string>
#include<vector>
#include<map>
//#include<list>
#include<queue>
#include<deque>
#include<algorithm>
//#include<numeric>
#include<utility>
#include<complex>
//#include<memory>
#include<functional>
#include<cassert>
#include<set>

const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int, int> pii;

const int MAXC = 100100;
const int MAXN = 101;
const int INF = 1e9;
int dp[MAXC];
int C, N;
int a[MAXN];

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> C;
    cin >> N;
    for (int i = 1; i <= N; i++) {
        cin >> a[i];
    }
    for (int i = 1; i <= C; i++) dp[i] = INF;
    for (int i = 1; i <= N; i++) {
        for (int j = 0; j < C; j++) {
            if (dp[j] < INF) {
                if (j+a[i] <= C) dp[j+a[i]] = min(dp[j+a[i]], 1+dp[j]);
            }
        }
    }
    int ans = dp[C];
    if (ans == INF) ans = -1;
    cout << ans << endl;
    return 0;
}