#include <bits/stdc++.h>
using namespace std;
#define REP(i, n) for(int(i)=0;(i)<(n);++(i))
#define in(T,V) T V;cin>>V;

const int LIM = 1000000;
int dp[111111];

int main(){
    in(int,C);
    in(int,N);
    REP(i,C+1) dp[i] = LIM; dp[0] = 0;
    REP(i,N){
        in(int,v);
        for(int j = v; j <= C; j++)
            dp[j] = min(dp[j], dp[j-v] + 1);
    }
    cout << (dp[C] >= LIM ? -1 : dp[C]) << endl;
}