#include <iostream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <string>
#include <cstdlib>
#include <climits>
#include <algorithm>
using namespace std;

const int maxn=1000000;
int n,m,a[maxn];
bool f;

int main()
{
	freopen("leader.in","r",stdin);
	freopen("leader.out","w",stdout); 
	
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++)
	{
		int x;
		scanf("%d",&x);
		a[x]++;
	}
	for(int i=1;i<=maxn;i++)
	{
		if(a[i]>m/2)
		{
			f=true;
			printf("%d\n",i);
		}
	}
	if(!f)
	{
		cout<<-1<<endl;
	}
				
	return 0; 
}