#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
 int a;
 int n;
 cin >> n;
 vector<int> v;
 for (int i = 0; i < n; i++) {
  cin >> a;
  v.push_back(a);
 }
 n = 0;
 sort(v.rbegin(), v.rend());
 for (int i = v.size()-1; i > (v.size()-2) / 2; i--)
  n += (v[i]+1)/2;
 cout << n << endl;
}

You should iterate from v.begin to v.end. No the reverse way.