#include <bits/stdc++.h>
using namespace std;
int main() {
  string s1, s2;
  cin >> s1;
  cin >> s2;
  int h1 = ((s1[0] - '0') * 10) + (s1[1] - '0');
  int m1 = ((s1[3] - '0') * 10) + (s1[4] - '0');
  int h2 = ((s2[0] - '0') * 10) + (s2[1] - '0');
  int m2 = ((s2[3] - '0') * 10) + (s2[4] - '0');
  int ct1 = h1 * 60 + m1;
  int ct2 = h2 * 60 + m2;
  int ans = (ct2 + ct1) / 2;
  int h = ans / 60;
  int m = ans % 60;
  if (h < 10)
    cout << '0' << h << ":";
  else
    cout << h << ":";
  if (m < 10)
    cout << '0' << m;
  else
    cout << m;
}
