#include <bits/stdc++.h>
int main() {
  int h1, h2, h3, m1, m2, m3, sum1, sum2;
  scanf("%d:%d", &h1, &m1);
  sum1 = h1 * 60 + m1;
  scanf("%d:%d", &h2, &m2);
  sum2 = h2 * 60 + m2;
  h3 = (sum1 + sum2) / 2 / 60;
  m3 = ((sum1 + sum2) / 2) % 60;
  printf("%02d:%02d", h3, m3);
  return 0;
}
