#include <bits/stdc++.h>
using namespace std;
ifstream fin("elmaj.in");
ofstream fout("elmaj.out");
int n,m ,v[1000006], i, j;
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<=n-n/2;i++)
        if(v[i]==v[i+n/2])
    {
        fout<<v[i];
        return 0;
    }
    fout<<-1;
    return 0;
}