Overview

This problem asks you to calculate the total travel time for patrols that involve going back and forth across \(N\) checkpoints arranged in a straight line.

Analysis

Takahashi must travel from checkpoint \(N\) (the waiting station) to checkpoint \(1\) each time, and then return to the waiting station. The one-way travel distance covers \(N - 1\) checkpoints, so a round trip takes \(2(N - 1)\) seconds.

Since the alarm rings \(M\) times, this “round trip” is performed \(M\) times, so the total time is simply \(2(N - 1) \times M\).

A naive approach, such as simulating and adding up the travel time for each alarm, would result in TLE (Time Limit Exceeded) since \(M\) can be up to \(10^9\). However, since the pattern is fixed in this problem, we can compute the answer directly using a formula.

Algorithm

1. Read \(N\) and \(M\) from the input.
2. Calculate the total time by multiplying the round trip time \(2(N - 1)\) by the number of alarms \(M\).
3. Output the result.

This is a simple arithmetic calculation, and there is no need to use loops.

Complexity

• Time complexity: \(O(1)\)
• Space complexity: \(O(1)\)

Implementation Notes

• No particularly difficult algorithms are needed. Just read the input and compute using the given formula.
• The range of values (on the order of \(10^9\)) requires attention to overflow, but this is not an issue in Python.

## Source Code

```python
N, M = map(int, input().split())
total_time = 2 * (N - 1) * M
print(total_time)

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