#include <bits/stdc++.h>
using namespace std;
int main() {
  int h1, m1, h2, m2;
  scanf("%d:%d", &h1, &m1);
  scanf("%d:%d", &h2, &m2);
  int tim1 = h1 * 60 + m1;
  int tim2 = h2 * 60 + m2;
  int tim = tim1 + tim2;
  tim /= 2;
  int h3 = tim / 60;
  int m3 = tim % 60;
  printf("%02d:%02d", h3, m3);
  return 0;
}
