#include <bits/stdc++.h>
using namespace std;
int main() {
  int h, m, h1, m1;
  char t, o;
  cin >> t >> o;
  int p, q;
  p = t - '0';
  q = o - '0';
  h = 10 * p + q;
  char s;
  cin >> s;
  cin >> t >> o;
  p = t - '0';
  q = o - '0';
  m = 10 * (int)p + (int)q;
  int total1 = h * 60 + m;
  cin >> t >> o;
  p = t - '0';
  q = o - '0';
  h1 = 10 * (int)p + (int)q;
  ;
  cin >> s;
  cin >> t >> o;
  p = t - '0';
  q = o - '0';
  m1 = 10 * (int)p + (int)q;
  ;
  int total2 = h1 * 60 + m1;
  int ans = (total2 - total1) / 2 + total1;
  int ha = ans / 60;
  int ma = ans - ha * 60;
  if (ha / 10 == 0 && ma / 10 == 0)
    cout << "0" << ha << ":"
         << "0" << ma << endl;
  if (ha / 10 != 0 && ma / 10 == 0)
    cout << ha << ":"
         << "0" << ma << endl;
  if (ha / 10 == 0 && ma / 10 != 0) cout << "0" << ha << ":" << ma << endl;
  if (ha / 10 != 0 && ma / 10 != 0) cout << ha << ":" << ma << endl;
}
