#include <iostream>
#include <cstdio>
#include <map>
using namespace std;

int n,m,x;
map<int,int> a;
map<int,int>::iterator it;
int ans,p;

int main()
{
	freopen("leader.in","r",stdin);
	freopen("leader.out","w",stdout);
	
	scanf("%d%d",&n,&m);
	for (int k=1; k<=m; k++)
	{
		scanf("%d",&x);
		a[x]++;
	}
	for (it=a.begin(); it!=a.end(); it++)
	{
		if (it->second > ans)
		{
			ans=it->second;
			p=it->first;
		}
	}
	if (ans>m/2)
		cout<<p<<endl;
	else
		cout<<-1<<endl;
	return 0;
}