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

typedef long long ll;

#define MOD 1000000007


int main()
{  
    int c,n;
    int a[100];
    ll dp[101][100001];
    cin >> c >> n; 
    fill(a,a+100,-1);//invalid error on sort
    rep(i,n)
    {
        cin >> a[i];
    }
    rep(i,10)
    {
        rep(j,100)
        {
            dp[i][j] = 1000000;
        }
    }
    dp[0][0] = 0;
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < c+1; j++)
        {
            if (j < a[i])
            {
                dp[i+1][j]= dp[i][j];
            } else
            {
                dp[i+1][j] = min(dp[i][j], dp[i+1][max(0,j-a[i])] + 1 );
            }
        }
    }
    if (dp[n][c] != 1000000)
    {
        cout << dp[n][c] << endl;
        return 0;
    }
    cout << "-1" << endl;
    return 0;
}