#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <ctime>
#include <cassert>
#include <climits>
#include <cstdlib>
#include <algorithm>
#include <set>
#include <map>
#include <vector>
#include <queue>
#include <stack>
#include <list>
#include <sstream>
#include <string>
using namespace std;

int n,m,x;
map<int,int> a;
int main()
{
	freopen("leader.in","r",stdin);
	freopen("leader.out","w",stdout);
	
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++)
	{
		scanf("%d",&x);
		a[x]++;
	}
	bool f=false;
	for(map<int,int>::iterator it=a.begin(); it!=a.end();it++)
	{
		if(it->second>m/2)
		{
			cout<<it->first<<' ';
			f=true;
		}
	}
	if(!f) cout<<-1<<endl;
	return 0; 
}