import java.util.HashMap;

import java.util.Iterator;

import java.util.Map;

import java.util.Map.Entry;

public class EvenOccuringElement {

public static void main(String[] args) {

EvenOccuringElement eoe = new EvenOccuringElement();

int[] input = { 1, 2, 3, 3, 3, 4, 4, 4, 5, 6 };

Integer evenElement = eoe.getElement(input);

if (evenElement != null)

System.out.println(evenElement);

}

public Integer getElement(int[] input) {

HashMap<Integer, Integer> counter = new HashMap<Integer, Integer>();

for (int i = 0; i < input.length; i++) {

if (counter.containsKey(input[i]))

counter.put(input[i], counter.get(input[i]) + 1);

else

counter.put(input[i], 1);

}

Iterator<Entry<Integer, Integer>> it = counter.entrySet().iterator();

while (it.hasNext()) {

Map.Entry<Integer, Integer> pairs = (Entry<Integer, Integer>) it

.next();

if (((Integer) pairs.getValue() % 2) == 0)

return (Integer) pairs.getKey();

}

return null;

}

}