#include <bits/stdc++.h>
using namespace std;
int main() {
  int h1, m1;
  scanf("%d:%d", &h1, &m1);
  int h2, m2;
  scanf("%d:%d", &h2, &m2);
  int t1 = h1 * 60 + m1;
  int t2 = h2 * 60 + m2;
  int t3 = (t1 + t2) / 2;
  printf("%02d:%02d\n", t3 / 60, t3 % 60);
  return 0;
}
