PROGRAMMING:Calculate train running time
According to the train's departure time and arrival time, we need to write a program to calculate the time of the whole journey.
###Input format:
Input two 4-digit positive integers in one line, separated by spaces, indicating the departure time and arrival time of the train respectively. The format of each time is 2-digit hours (00-23) and 2-digit minutes (00-59), assuming that the departure and arrival are on the same day.
###Output format:
Output the travel time in one line in the format of "HH: mm", where HH is 2-bit hours and MM is 2-bit minutes.
###Input example:
```in
1201 1530
```
###Output example:
```out
03:29
```
answer：If there is no answer, please comment
###Input format:
Input two 4-digit positive integers in one line, separated by spaces, indicating the departure time and arrival time of the train respectively. The format of each time is 2-digit hours (00-23) and 2-digit minutes (00-59), assuming that the departure and arrival are on the same day.
###Output format:
Output the travel time in one line in the format of "HH: mm", where HH is 2-bit hours and MM is 2-bit minutes.
###Input example:
```in
1201 1530
```
###Output example:
```out
03:29
```
answer：If there is no answer, please comment