Compute Productive Work Time

Given a series of time-stamped events representing work and break periods, compute the total productive time worked by an employee in minutes.

The events are provided in chronological order and include the following commands:

• start t: Employee starts working at time \( t \).
• break t: Employee begins a break at time \( t \). The work segment ends at this moment.
• return t: Employee returns from a break at time \( t \). A new work segment begins immediately.
• stop t: Employee stops working at time \( t \).

The total productive time is the sum of all work periods excluding break times.

inputFormat

The input is read from stdin and follows this format:

1. The first line contains an integer \( n \) which is the number of events.
2. The next \( n \) lines each contain an event represented as two tokens separated by a space: an action (one of start, break, return, or stop) and a non-negative integer representing time in minutes.

outputFormat

Output the total productive time worked in minutes as a single integer to stdout.

4
start 0
break 30
return 45
stop 90

75