import java.util.*;
 
public class Main {
    static int countPairsWithSum(int[] b, int k) {
		int count = 0;
        Set<Integer> seen = new HashSet<>();
 
        for (int num : b) {
            if (seen.contains(k - num)) {
                count++;
            }
            seen.add(num);
        }
        return count;
 
    }
 
    public static void main(String[] args) {
        int[] b = {1, 2, 3, 4, 5};
        int k = 6;
        int count = countPairsWithSum(b, k);
 
        System.out.println("Count of pairs with sum " + k + " is: " + count);
    }
}