Problem:
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The Number of Inversions

For a given sequence $A = \{a_0, a_1, ... a_{n-1}\}$, the number of pairs $(i, j)$ where $a_i > a_j$ and $i < j$, is called the number of inversions. The number of inversions is equal to the number of swaps of Bubble Sort defined in the following program:

bubbleSort(A)
cnt = 0 // the number of inversions
for i = 0 to A.length-1
for j = A.length-1 downto i+1
if A[j] < A[j-1]
swap(A[j], A[j-1])
cnt++

return cnt

For the given sequence $A$, print the number of inversions of $A$. Note that you should not use the above program, which brings Time Limit Exceeded.

Input

In the first line, an integer $n$, the number of elements in $A$, is given. In the second line, the elements $a_i$ ($i = 0, 1, .. n-1$) are given separated by space characters.

output

Print the number of inversions in a line.

Constraints

$ 1 \leq n \leq 200,000$

$ 0 \leq a_i \leq 10^9$

$a_i$ are all different

Sample Input 1

5
3 5 2 1 4

Sample Output 1

6

Sample Input 2

3
3 1 2

Sample Output 2

2

Solution in C (judge verdict: Time Limit Exceeded)

#include<stdio.h>
#define MAX 200000

int bubbleSort(int *);

int n;

int main()
{
  int i;
  int A[MAX];

  scanf("%d",&n);
  for(i = 0;i < n;i++){
    scanf("%d",&A[i]);
  }

  printf("%d\n",bubbleSort(A));

  return 0;
}

int bubbleSort(int *A)
{
  int cnt = 0,i,j,tmp;
  for(i = 0;i < n;i++){
    for(j = n-1;j >= i+1;j--){
      if(A[j] < A[j-1]){
	tmp = A[j];
	A[j] = A[j-1];
	A[j-1] = tmp;
	cnt++;
      }
    }
  }
  return cnt;
}