import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.Arrays;
import java.util.concurrent.*;
import java.util.regex.*;
import java.util.Collections;

public class Solution {

    // Complete the sockMerchant function below.
    static int sockMerchant(int n, int[] ar) {


     List<Integer> myArray = new ArrayList<Integer>();
for (int i : ar)
{
    myArray.add(i);
}

     int noOfPairs=0;
     for(int i=0;i<myArray.size()-1;i++){
         for(int j=i+1;j<myArray.size();j++){
             if(myArray.get(i)==myArray.get(j) ){
              noOfPairs++;
              myArray.remove(j);
             myArray.remove(i);
             i=0;
             j=0;

             }



         }

     }
     return noOfPairs;
    }




    private static final Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) throws IOException {
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        int n = scanner.nextInt();
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

        int[] ar = new int[n];

        String[] arItems = scanner.nextLine().split(" ");
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

        for (int i = 0; i < n; i++) {
            int arItem = Integer.parseInt(arItems[i]);
            ar[i] = arItem;
        }

        int result = sockMerchant(n, ar);

        bufferedWriter.write(String.valueOf(result));
        bufferedWriter.newLine();

        bufferedWriter.close();

        scanner.close();
    }
}