Inversion Count (APCS 2018-06 Expert)

2.0s 256M

Count index pairs \((i,j)\) with \(i<j\) and \(a_i>a_j\). Different index pairs count separately, even if their values coincide.

Input Format

Read \(n\), then the \(n\) values.

Output Format

Print the inversion count.

Constraints

\(1\le n\le100000\), \(0\le a_i\le1000000\).

Sample Input

6
3 1 9 8 9 2

Sample Output

6

Source

APCS 2018-06 public archive version: tcirc:d064。

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