We can determine how "out of order" an array A is by counting the number of inversions it has. Two elements A[i] and A[j] form an inversion if A[i] > A[j] but i < j. That is, a smaller element appears after the larger element.

Write a function `solve`

that have the following parameter(s):

1.) *a = an array of integers*

**Example**

Input:

`[2, 4, 1, 3, 5]`

Output:

`3`

**Example**

Input:

`[1, 2, 3, 4, 5]`

Output:

`0`

**Constraints**

• The length of an array should be greater than 0 and less than 800.

• The elements of an array should be greater than 0 and less than 1000.