#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;

int main(){

    long long C, N;
    cin >> C >> N;
    vector<long long> a(N+1);
    for (int i=1; i<=N; i++) cin >> a[i];
    vector<vector<long long>> dp(N+1, vector<long long>(C+1, 1e18));
    for (int i=0; i<=N; i++) dp[i][0] = 0;

    for (int i=1; i<=N; i++){
        for (int j=1; j<=C; j++){
            dp[i][j] = min(dp[i][j], dp[i-1][j]);
            if (j >= a[i]) dp[i][j] = min(dp[i][j], dp[i][j-a[i]] + 1);
        }
    }

    cout << (dp[N][C] == 1e18 ? -1 : dp[N][C]) << endl;

    return 0;
}