No.3048 Swing
suisen
37zigen
rin204
問題文最終更新日: 2025-01-21 14:41:30
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yukicoder contest 459
(順位表)
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Problem Statement
You are given integers $x,n$.
Define the sequence $X=(X_0,X_1,\ldots,X_n)$ as follows.
$$\begin{aligned} X _ 0 & {} = x,\cr X _ i & {} = \begin{cases} X _ {i - 1} + i & (\text{if } X _ {i - 1} \leq 0) \cr X _ {i - 1} - i & (\text{otherwise}) \end{cases} & (1 \leq i \leq n). \end{aligned}$$
Find $X _ n$.
Input
The input is given from Standard Input in the following format.
$x$ $n$
- All input values are integers.
- $-10 ^ {18} \leq x \leq 10 ^ {18}$
- $1 \leq n \leq 10 ^ {18}$
Output
Print $X_n$ on 1 line, followed by a newline.
Sample
Sample 1
Input
2 3
Output
2
This input corresponds to $x=2,\ n=3$. $X_0,X_1,X_2,X_3$ are determined as follows.
- $X_0 = x = 2$
- Since $X_0 \gt 0$, $X_1 = X_0 - 1 = 1$
- Since $X_1 \gt 0$, $X_2 = X_1 - 2 = -1$
- Since $X_2 \leq 0$, $X_3 = X_2 + 3 = 2$
Therefore, print $2$ as the answer.
Sample 2
Input
10 3
Output
4
Sample 3
Input
1000000000000000000 1000000000000000000
Output
-499999999472363922
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