#include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<map>
#include<string>
#include<algorithm>
#include<functional>
using namespace std;
#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 (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define INF 1<<30
#define MP make_pair
#define mp make_pair
#define pb push_back
#define PB push_back
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define ll long long
#define ull unsigned long long

ll dp[110][100010];

int main(){
	int C;int n;cin>>C>>n;
	int a[n];
	REP(i,n) cin>>a[i];
 	fill((ll*)dp,(ll*)dp+n*(C+1),INF);
	dp[0][0]=0;
	
	REP(i,n){
		REP(j,C+1){
			if(j<a[i]) dp[i+1][j]=dp[i][j];
			else dp[i+1][j]=min(dp[i][j], dp[i+1][j-a[i]]+1);
		}
	}
	if(dp[n][C]==INF) {cout<<-1<<endl;return 0;}
	cout<<dp[n][C]<<endl;
	return 0;
}