#include <bits/stdc++.h>
using namespace std;
int main() {
  string s1;
  string s2;
  cin >> s1;
  cin >> s2;
  char s[5];
  int a[4];
  int b[4];
  string q;
  a[0] = s1[0] - '0';
  a[1] = s1[1] - '0';
  a[2] = s1[3] - '0';
  a[3] = s1[4] - '0';
  b[0] = s2[0] - '0';
  b[1] = s2[1] - '0';
  b[2] = s2[3] - '0';
  b[3] = s2[4] - '0';
  int m1 = abs((a[0] * 10 + a[1]) - 0) * 60 + (a[2] * 10 + a[3]);
  int m2 = abs((b[0] * 10 + b[1]) - 0) * 60 + (b[2] * 10 + b[3]);
  int M = (m1 + m2) / 2;
  int X = M / 60;
  int Y = M % 60;
  cout << X / 10 << X % 10 << ':' << Y / 10 << Y % 10;
}
