#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  string p1, p2;
  cin >> p1;
  cin >> p2;
  int h1 = stoi(p1.substr(0, 2));
  int h2 = stoi(p2.substr(0, 2));
  int m1 = stoi(p1.substr(3, 2));
  int m2 = stoi(p2.substr(3, 2));
  int avghr = (h1 + h2) * 30;
  int avgmin = (m1 + m2) / 2;
  int hrs = (avghr + avgmin) / 60;
  int mins = (avghr + avgmin) % 60;
  if (hrs < 10) {
    if (mins < 10) {
      cout << "0" << hrs << ":0" << mins;
    } else {
      cout << "0" << hrs << ":" << mins;
    }
  } else {
    if (mins < 10) {
      cout << hrs << ":0" << mins;
    } else {
      cout << hrs << ":" << mins;
    }
  }
  return 0;
}
