#include<stdio.h>

int main()
{
	unsigned long n,v[1000000],i,j,a,s;
	freopen("elmaj.in","r",stdin);
	freopen("elmaj.out","w",stdout);
	scanf("%ld",&n);
	for(i=0;i<n;i++)
	scanf("%ld",&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)
		printf("%ld%ld",v[s],a);
	else
		printf("%d",-1);
	return 0;
}