编程题：Calculate the duration of train operation

According to the departure time and arrival time of the train, write a program to calculate the time used for the whole journey.

### Input Specification:

Input two 4-digit positive integers in one line, separated by a space, representing 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). It is assumed that departure and arrival are in the same day.

### Output Specification:

Output the time used for the trip in the format of "hh: mm", where hh is the 2-digit hours and mm is the 2-digit minutes.

### Sample Input #1:

in
1015 1230


### Sample Output #1:

out
02:15


### Sample Input #2:

in
0958 2103


### Sample Output #2:

out
11:05











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