#include <bits/stdc++.h>
using namespace std;
int main() {
  int h1, m1, h2, m2, s1, s2, h, m;
  scanf("%d:%d", &h1, &m1);
  scanf("%d:%d", &h2, &m2);
  s1 = h1 * 60 + m1;
  s2 = h2 * 60 + m2;
  m = (s1 + s2) / 2;
  h = m / 60;
  m = m % 60;
  printf("%02d:%02d\n", h, m);
  return 0;
}
