/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
import java.util.HashMap;
 
class Ideone
{
	static long countPairs(int[] a)
	{
		var m = new  HashMap<Integer, Integer>();
		for (var x : a)
		{
			m.compute(x, (, v) -> (v == null) ? 1 : v + 1);
		}
		return m.values().stream().filter((v) -> v == 2).count();
	}
	public static void main (String[] args) throws java.lang.Exception
	{
		System.out.println(countPairs(new int[]{1 ,2 ,0 , 0, 1}));
	}
}

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