#include<fstream.h>

using namespace std;

int main()
{
	unsigned long long n,v[1000000],i,j,a,s;
	ifstream fin("elmaj.in");
	ofstream fout("elmaj.out");
	fin>>n;
	for(i=0;i<n;i++)
	fin>>v[i];
	for(i=1;i<n;i++)
	for(j=0;j<i;j++)
	if(v[j]>v[i]) 
	{a=v[i];v[i]=v[j];v[j]=a;}
	a=0;s=n/2;
	for(i=0;i<n;i++)
		if(v[s]==v[i]) a++;
	if(a>=s+1)
		fout<<v[i]<<a;
	else
		fout>>-1;
	return 0;
}