Airplane
The plane departs from city A at h_1 hours and m_1 minutes, according to the local time in city A, and arrives in city B at h_2 hours and m_2 minutes, based on the local time in city B. From city B, it departs at h_{3} hours and m_3 minutes (local time of city B, which may be on a different day) and returns to city A at h_4 hours and m_4 minutes (local time of city A). The duration of the flight is the same in both directions and is not zero. What is the duration of the flight in one direction? Provide your answer in hours and minutes, rounding up to the nearest whole minute if necessary.
Input
Each of the four lines contains the departure and arrival times in the format hh:mm, following the order specified in the problem statement; 0 ≤ h_j < 24, 0 ≤ m_j < 60.
Output
Output the flight duration in the format hh:mm. If there are multiple possible answers, provide the smallest one.