#include <bits/stdc++.h>
using namespace std;
int main() {
  long long a = 0, b = 0, c = 0, d = 0;
  scanf("%d:%d", &a, &c);
  scanf("%d:%d", &b, &d);
  long long p = a * 60 + c;
  long long k = b * 60 + d;
  p = (p + k) / 2;
  if ((p / 60) < 10)
    cout << 0 << p / 60 << ":";
  else
    cout << p / 60 << ":";
  if ((p % 60) < 10)
    cout << 0 << p % 60;
  else
    cout << p % 60;
  return 0;
}
