#include<bits/stdc++.h>
typedef long long ll;
using namespace std;
int INF = 1e9;
int MOD = 1e9+7;
int dp[100010];
main(){
    int C,N,A[100];
    cin >> C >> N;
    for(int i = 0;i < N;i++)cin >> A[i];
    fill(dp,dp+100010,INF);
    dp[0] = 0;
    for(int i = 0;i < N;i++){
        for(int j = 0;j < A[i];j++){
            for(int k = j+A[i];k <= 100000;k+=A[i]){
                dp[k] = min(dp[k],dp[k-A[i]]+1); 
            }
        }
    }
    if(dp[C] == INF)cout << -1 << endl;
    else cout << dp[C] << endl;
}