两个网站都通过

#include <iostream>
#include <algorithm>
using namespace std;
const int N = 1010;

int n;
int a[N];

int main()
{
    cin >> n;
    for(int i = 0; i < n; ++ i) cin >> a[i];

    nth_element(a, a + n / 2, a + n);

    int cnt1 = 0, cnt2 = 0;
    for(int i = 0; i < n; ++ i)
        if(a[i] > a[n / 2]) cnt1 ++;
        else if(a[i] < a[n / 2]) cnt2 ++;

    if(cnt1 == cnt2) cout << a[n / 2] << endl;
    else cout << -1 << endl;

    return 0;
}