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

int n,m;
map <int,int> a;
int ans;
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]++;
	}
	m/=2;
	map<int,int>::iterator it;
	ans=-1;
	for(it=a.begin();it!=a.end();it++)
	{
		int tt=(*it).second;
		//printf("%d\n",tt);
		if(tt>m)
		{
			ans=(*it).first;
			break;
		}
	}
	

	printf("%d",ans);
	return 0;
}