Exchange Cups

The store has a lot of cups, numbered 1-N on the shelf.

For example, there are 5 cups:
2 1 3 5 4

Ask to pick up 2 cups at a time and swap their positions.

After several times, the serial number of the cups is made:
1 2 3 4 5

For such a simple case, obviously, at least 2 swaps are required to reset.

The input format is two lines:

Line 1: A positive integer N (N < 10000) representing the number of bottles
Second line: N positive integers, separated by spaces, indicating the current arrangement of the bottles.

The output data is a positive integer in a row, indicating at least how many times to swap to complete the sorting.

Function Description
Complete the function exchange_cups in the editor below.
exchange_cups has the following parameter(s):

labels[label[0],...label[N-1]]: an array of integers

Constraints
N(N < 10000)