#include <bits/stdc++.h>
#include <cmath>
#include <climits>
#include <cstdio>

using namespace std;

#define endl '\n'
#define PB push_back
#define ALL(a)  (a).begin(),(a).end()
#define SZ(a) int((a).size())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n)  FOR(i,0,n)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define RBP(i,a) for(auto& i : a)
#define DEBUG(x) cout<<#x<<": "<<(x)<<endl
#define F first
#define S second
#define SNP string::npos
#define WRC(hoge,x) cout << "Case #" << (hoge)+1 << ": " << x << endl
#define ten(n) (LL)pow(10,n)
#define INF ten(8)

typedef pair<int,int> P;
typedef long long int LL;
typedef unsigned long long ULL;
typedef pair<LL,LL> LP;

void ios_init(){ ios::sync_with_stdio(false); cin.tie(0);	
	//cout.setf(ios::fixed);
	//cout.precision(12);
}

LL dp[100010];

int main()
{
	ios_init();
	int n,c;
	cin >> c;
	cin >> n;
	vector<int> a(n);
	REP(i,n) cin >> a[i];
	fill(dp,dp+c+1,-1);
	dp[0] = 0;
	REP(i,n){
		FOR(j,a[i],c+1){
			if(dp[j-a[i]] != -1){
				if(dp[j] != -1)	dp[j] = min(dp[j],dp[j-a[i]]+1);
				else dp[j] = dp[j-a[i]]+1;
			}
		}
	}
	cout << dp[c] << endl;
	return 0;
}