/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
		Map<Integer,Integer> map = new HashMap<>();
		int arr[] = {1,3,4,2,3,1,1};
		int count = 0;
		int n = arr.length;
		int k = 5;
		for(int i = 0;i<n;i++){
		int complement = k -arr[i];
		 if (map.containsKey(complement)) {
                count++;
            }
            map.put(arr[i],i);
		}
 
		System.out.println(count);
	}
}

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