import java.util.HashMap;

/**
 * MatchPairedColors
 */
public class MatchPairedColors {

  public static void main(String[] args) {

    int[] ar = { 1, 1, 1, 1, 3, 2, 2, 3, 4 };
    System.out.println(numberOfPairedSocks(ar));
  }

  private static int numberOfPairedSocks(int[] arr) {
    int numofP = 0;
    HashMap<Integer, Integer> socksCount = new HashMap<>();
    for (int sock : arr) {
      if (socksCount.containsKey(sock)) {
        socksCount.put(sock, socksCount.get(sock) + 1);
      } else {
        socksCount.put(sock, 1);
      }
    }

    for (int count : socksCount.values()) {
      numofP += count / 2;
    }
    return numofP;
  }
}