#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

int C, N, INF = INT_MAX;
vi A;

int main(){
    cin >> C >> N;
    A = vi(N);
    rep(i, N)scanf("%d", &A[i]);
    vi dp(C + 1, INF);
    dp[0] = 0;
    each(a, A)
        for(int i = 0; i <= C - a; ++i)
            if(dp[i]!=INF)
                smin(dp[i + a], dp[i] + 1);
    cout << (dp[C] != INF ? dp[C] : -1) << endl;
}