#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 h = h1 + h2 >> 1, m = m1 + m2 >> 1;
  if (h1 + h2 & 1) m += 30;
  h += m / 60, m %= 60;
  printf("%02d:%02d\n", h, m);
}
