#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

const int INF = INT_MAX / 2;

int main()
{
    int c, n;
    cin >> c >> n;
    vector<int> a(n);
    for(int i=0; i<n; ++i)
        cin >> a[i];

    vector<int> dp(c+1, INF);
    dp[0] = 0;
    for(int i=0; i<n; ++i){
        for(int j=a[i]; j<=c; ++j){
            dp[j] = min(dp[j], dp[j-a[i]] + 1);
        }
    }

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

    return 0;
}