#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    ll c, n;
    cin >> c >> n;
    ll a[n];
    rep(i,n) cin >> a[i];
    ll dp[c+1] = {};
    ll INF = 1001001001001001001;
    srep(i,1,c+1) dp[i] = INF;

    rep(i,n){
        rep(j,c+1-a[i]){
            dp[j+a[i]] = min(dp[j+a[i]], dp[j] + 1);
        }
    }

    if(dp[c] == INF) dp[c] = -1;
    cout << dp[c] << endl;
    return 0;
}