#define _USE_MATH_DEFINES
 
#include <iostream>
#include <iomanip>
 
#include <algorithm>
#include <cmath>
 
#include <string>
//#include <array>
#include <list>
#include <queue>
#include <vector>
#include <complex>
#include <set>
#include <map>
 
/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
 
#define PII pair<int,int>
/////////
typedef long long LL;
typedef long double LD;
/////////
using namespace::std;
/////////


int main(void){
    std::cin.tie(0); 
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed;//
    //cout << setprecision(10);//
	
	int C,N;
	cin>>C>>N;
	int A[100];
	rep(i,N){cin>>A[i];}
	sort( A,A+N, greater<int>() );
	const int dpmax = 100001;
	int dp[dpmax];
	rep(i,dpmax){
		dp[i] = 1<<28;
	}
	dp[0]=0;
	rep(i,dpmax){
		rep(j,N){
			if(i+A[j] < dpmax){
				dp[ i + A[j] ] = min( dp[i+A[j]] , dp[i]+1 );
			}
		}
	}
	if(dp[C] == 1<<28){
		P(-1);
	}else{
		P(dp[C]);
	}
    return 0;
}