//Zhandos Kapezov
#include <iostream>
#include <math.h>
#include <cmath>
#include <vector>
#include <utility>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <fstream>
#include <string>
#include <string.h>
#include <sstream>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <deque>
#include <limits>
#include <list>
#include <functional>
#include <bitset>
#include <numeric>
#include <iomanip>
#include <ctime>
#include <ctype.h>

using namespace std;
typedef long long ll;

#define F first
#define S second
#define pb push_back
#define mp make_pair
#define sz size()
#define sqr(x) ((x)*(x))
#define INF numeric_limits<int>::max()

int bit(int x, int i) {
    return (x>>i)&1;
}

int main()
{
    #ifndef ONLINE_JUDGE
        freopen("input.txt","rt",stdin);
        freopen("output.txt","wt",stdout);
    #endif
    cin>>x>>n; res=-1; pp=1;
    for (int i=0; i<n; i++) pp*=x;
    for (int i=0; i<n; i++) cin>>a[i];

    for (int p=0; p<pp; p++) {
        cur=p; now=0; j=0; nn=0;
        while (cur) {
            now+=a[j]*(cur%3);
            nn+=cur%3;
            cur/=3; j++;
        }
        if (now>x) res=0;
        if (now==x) {
            if (!res) res=nn; else
            res=min(res, nn);
        }
    }
    cout<<res;
    return 0;
}