给定 $n$，求下式的值：
$$\sum_{i=1}^{n-1} i \oplus (n - i)$$
其中 $\oplus$ 表示按位异或运算。
输入格式
输入包含一个整数 $n$ ($2 \le n < 10^{500}$)。
输出格式
输出一个整数，即该求和的结果。
样例
输入 1
3
输出 1
6
输入 2
4
输出 2
4
QOJ.ac
QOJ
実行時間制限： 1 s
メモリ制限： 524288 MB
満点： 100
ハック可能 ✓
#13231. 异或
統計
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