#include"bits/stdc++.h"

//#include<bits/stdc++.h>
using namespace std;
#define print(x) cout<<x<<endl;
#define rep(i,a,b) for(int i=a;i<b;i++)
#define REP(i,a) for(int i=0;i<a;i++)
typedef long long ll;
typedef pair<int, int> PI;
typedef pair<int, PI> V;
const ll mod = 100000000;

int c, n, a[102];
int dp[102] = {};


int main() {
	REP(i, 102)REP(j, 100002)dp[i] = mod;
	cin >> c; cin >> n;
	REP(i, n)cin >> a[i];
	dp[0] = 0;
	REP(i, c+1) {
		REP(j, n) {
			dp[i] = min(dp[i],dp[i - a[j]]+1);
		}
	}
	int ans = dp[c] == mod ? -1 : dp[c];
	print(ans);
}