import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;
public class SockMerchant{
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int n = in.nextInt();
int c[] = new int[n];
for(int c_i=0; c_i < n; c_i++){
c[c_i] = in.nextInt();
}
Arrays.sort(c);
int a=c[0],pairs=0;
boolean flag=true;
for(int i=1;i