#include <bits/stdc++.h>
using namespace std;

typedef long long ill;
ill arr[250000];
int main()
{
    int n;
    cin >> n;
    for(int i = 0; i < n; ++i) cin >> arr[i];

    nth_element(arr,arr+n/2,arr+n);
    double ans = (double)arr[(n/2)];

    if (n & 1){
        printf("%0.1lf\n",ans);
    }
    else {
        nth_element(arr,arr+(n/2)-1,arr+n);
        ans += (double)arr[(n/2)-1];
        printf("%0.1lf\n",ans/2.0);
    }
    return 0;
}

Can somebody tell me the problem ....