Overview

Process the changes in the neighborhood association’s activity funds for each event, and find the difference between the final theoretical value and the actual balance.

Analysis

This problem is a simple simulation problem where you just calculate the increase and decrease of funds for each event in order.

Each event is one of the following two types:

• Membership event (\(e_i = 1\)): Add \(v_i\) yen to the activity funds.
• Purchase event (\(e_i = 2\)): Subtract \(v_i \times P\) yen from the activity funds.

By performing these operations in order, starting from the initial balance \(S\), we obtain the final theoretical value, and subtracting the actual balance \(R\) from it gives us the answer.

There is nothing particularly difficult about the straightforward approach — it can be solved by simply processing events sequentially from the beginning. Looking at the constraints, the number of events \(M\) is at most \(2 \times 10^5\), but since each event can be processed in constant time, the overall computation is sufficiently fast.

However, since the fund balance and the final theoretical value can become very large (on the order of \(10^{18}\)), languages like Python handle this fine with their default integer type, but in C++ and similar languages, using long long is necessary.

Algorithm

1. Prepare a variable total initialized to the initial balance \(S\).
2. Process each event as follows:
   • If it is a membership event (\(e_i = 1\)), then total += v
   • If it is a purchase event (\(e_i = 2\)), then total -= v * P
3. Subtract the actual balance \(R\) from the final total and output the result.

Complexity

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

Implementation Notes

• Since you only need to process each event in order, just use branching inside a loop.

• Don’t forget to multiply by the unit price \(P\) for purchase events.

• In Python, there is no limit on integer range, so large values can be handled as-is.

  Source Code

S, P, R = map(int, input().split())
M = int(input())
total = S
for _ in range(M):
    e, v = map(int, input().split())
    if e == 1:
        total += v
    else:
        total -= v * P
print(total - R)

This editorial was generated by qwen3-coder-480b.