How do you solve the problem of a sock merchant?

Problem statement:
John works at a clothing store. He has a large pile of socks that he must pair by color for sale. Given an array of integers representing the color of each sock, determine how many pairs of socks with matching colors there are.

For example, there are n = 7 socks with colors ar = [1,2,1,2,1,3,2] . There is one pair of color 1 and one of color 2. There are three odd socks left, one of each color. The number of pairs is 2.

Input Format:
The first line contains an integer n, the number of socks represented in ar. 

The second line contains n space-separated integers describing the colors ar[i] of the socks in the pile.

Constraints:
1 <= n <=100
1 <= ar[i] <= 100 where 0 <= i < n

Output Format:
Return the total number of matching pairs of socks that John can sell.

Sample Input:
9
10 20 20 10 10 30 50 10 20

Sample Output:
3

1. // sockMerchant function below.
2.     static int sockMerchant(int n, int[] ar) {        
3.         int count = 0;
4.         Arrays.sort(ar);
5.         for(int i = 0; i < ar.length-1; i++)
6.         {
7.             if(ar[i] == ar[i+1])
8.             {
9.                 count = count+1; // count++;
10.                 //i+=1;
11.                 i = i+1;        
12.             }
13.         }        
14.         return count;
15.     }