#include<sstream>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
#include<bitset>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())
#define indexOf(v,x) (find(all(v),x)-v.begin())


int dp[100001];

int main(){
	memset(dp,-1,sizeof(dp));
	dp[0]=0;
	int c,n,a[100];
	cin>>c>>n;
	rep(i,n)cin>>a[i];
	rep(i,c){
		if(dp[i]==-1)continue;
		rep(j,n){
			if(c<i+a[j])continue;
			if(dp[i+a[j]]==-1||dp[i]+1<dp[i+a[j]])
				dp[i+a[j]]=dp[i]+1;
		}
	}
	cout<<dp[c]<<endl;
	return 0;
}