#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<climits>
#include<cstdlib>
#include<ctime>
#include<cctype>
#include<algorithm>
#include<set>
#include<map>
#include<vector>
#include<stack>
#include<queue>
#include<deque>
#include<string>
#include<sstream>
#include<iomanip>
#define mint map<int,int>::iterator
using namespace std;
//=====================struct declaration======================

//=====================var declarartion========================
map<int,int> a;

int n,m;
//=====================function declaration====================
int getint();
//=====================main code===============================
int main()
{
	freopen("leader.in","r",stdin);
	freopen("leader.out","w",stdout);
	
	n=getint(); m=getint();
	for(int ii=1; ii<=m; ii++)
	{
		int x;
		x=getint();
		a[x]++; 
	}
	
	for(mint it=a.begin(); it!=a.end(); it++)
	{
		if(it->second>m/2)
		{
			printf("%d\n",*it);
			return 0;
		}
	}
	
	printf("-1\n");
	
	return 0;
}
//=====================function code===========================
int getint()
{
	int x=0,s=1;
	char ch=' ';
	while(ch<'0' || ch>'9')
	{
		ch=getchar();
		if(ch=='-') s=-1;
	}
	while(ch>='0' && ch<='9')
	{
		x=x*10+ch-'0';
		ch=getchar();
	}
	return x*s;
}