#include <algorithm>
#include <array>
#include <sstream>
#include <cstdio>
#include <functional>
#include <cstdlib>
#include <cctype>
#include <ostream>
#include<complex>
#include <cmath>
#include <iostream>
#include <stack>
#include <fstream>
#include <queue>
#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <bitset>
#include <iomanip>
#include <string>
#include <vector>
#include <string>
using namespace std;
#define OB (bitset<32>)
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define ALLOF(c) begin(), (c),end()

typedef long long ll;

#define PI acos(-1)
#define EPS 0.000000001
#define MOD 1000000007


int main()
{  
    int dp[105][100001];
    int c;
    int n;
    int a[100];
    cin >> c >> n;
    fill(a,a+100,-1);//invalid error on sort
    rep(i,105)
    {
        rep(j,100001)
        {
            dp[i][j] = 10000000;
        }
    }
    /* なんでRE起きんねん
    rep(i,n)
    {
        cin >> a[i];
    }
    sort(a,a+100,greater<int>());
    dp[0][0] = 0;
    rep(i,n)
    {
        rep(j,c+1)
        {
            if (j <a[i])
            {
                dp[i+1][j]= dp[i][j];
            }
            else
            {
                dp[i+1][j] = min(dp[i][j],dp[i+1][j-a[i]]+1);
            }
        }
    }
    if (dp[n][c]!= MOD)
    {
        cout << dp[n][c] << endl;
        return 0;
    }*/
    cout << "-1" << endl;
    return 0;
}