#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)n;++i)
#define each(a, b) for(auto (a): (b))
#define all(v) (v).begin(),(v).end()
#define fi first
#define se second
#define pb push_back
#define show(x) cout <<#x<<" = "<<(x)<<endl
#define spair(p) cout <<#p<<": "<<p.fi<<" "<<p.se<<endl
#define svec(v) cout<<#v<<":";rep(kbrni,v.size())cout<<" "<<v[kbrni];cout<<endl
#define sset(s) cout<<#s<<":";each(kbrni,s)cout <<" "<<kbrni;cout<<endl

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 100005;

int dp[MAX_N];

int main()
{
    int C,n;
    cin >> C >> n;
    vector<int> a(n);
    rep(i,n){
        cin >> a[i];
    }
    rep(i,C+1){
        dp[i] = INF;
    }
    dp[0] = 0;
    rep(i,n){
        rep(j,C+1){
            if(j >= a[i]){
                dp[j] = min(dp[j],dp[j-a[i]]+1);
            }
        }
    }
    if(dp[C] != INF){
        cout << dp[C] << "\n";
    }else{
        cout << "-1\n";
    }
    return 0;
}