#include <bits/stdc++.h>
using namespace std;
int main() {
  string s, e;
  cin >> s >> e;
  int h1, h2, m1, m2;
  h1 = (s[0] - 48) * 10;
  h2 = (e[0] - 48) * 10;
  h1 = h1 + s[1] - 48;
  h2 = h2 + e[1] - 48;
  m1 = (s[3] - 48) * 10;
  m2 = (e[3] - 48) * 10;
  m1 = m1 + s[4] - 48;
  m2 = m2 + e[4] - 48;
  int a, b, c;
  a = (h1 * 60) + m1;
  b = (h2 * 60) + m2;
  c = (a + b) / 2;
  if (c / 60 < 10)
    cout << "0" << c / 60;
  else
    cout << c / 60;
  cout << ":";
  if (c % 60 < 10)
    cout << "0" << c % 60;
  else
    cout << c % 60;
}
