#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <numeric>
#include <functional>
#include <cmath>
#include <queue>
#include <stack>

#define repd(i,a,b) for (int i=(a);i<(b);i++)
#define rep(i,n) repd(i,0,n)
typedef long long ll;

using namespace std;


int inputValue(){
    int a;
    cin >> a;
    return a;
};

void inputArray(int * p, int a){
    rep(i, a){
        cin >> p[i];
    }
};

void inputVector(vector<int> * p, int a){
    rep(i, a){
        int input;
        cin >> input;
        p -> push_back(input);
    }
}

template <typename T>
void output(T a, int precision) {
    if(precision > 0){
        cout << setprecision(precision)  << a << "\n";
    }
    else{
        cout << a << "\n";
    }
}

int dp[1000000] = {-1};


int main(int argc, const char * argv[]) {
    
    // source code
    int C = inputValue();
    int N = inputValue();
    vector<int> a;
    rep(i, N){
        a.push_back(inputValue());
    }
    
    dp[0] = 0;
    
    
    repd(i, 1, C + 1){
        int m = 10000000;
        rep(j, N){
            if (i >= a[j]) {
                m = min(m, dp[i - a[j]] + 1);
            }
        }
        dp[i] = m;
    }
    
    output((dp[C] == 10000000) ? -1 : dp[C], 0);
    
    
    
    return 0;
}