import java.util.Scanner;
import java.util.HashSet;
import java.util.ArrayList;

public class TreasurePairs {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        if (Scanner.hasNextInt()) {
            System.out.println("Invalid input");
            scanner.close();
            return;
        }
        int n = scanner.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            if (scanner.hasNextInt()) {
                arr[i] = scanner.nextInt();
            } else {
                System.out.println("Invalid input");
                scanner.close();
                return;
            }
        }
        if (!scanner.hasNextInt()) {
            System.out.println("Invalid input");
            scanner.close();
            return;
        }
        int target = scanner.nextInt();
        scanner.close();
        HashSet<String> uniquePairs = new HashSet<>();
        ArrayList<String> pairsList = new ArrayList<>();
        boolean found = false;
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                if (arr[i] + arr[j] == target) {
                    int first = Math.min(arr[i], arr[j]);
                    int second = Math.max(arr[i], arr[j]);
                    String pair = first + "," + second;
                    if (!uniquePairs.contains(pair)) {
                        uniquePairs.add(pair);
                        pairsList.add(pair);
                        found = true;
                    }
                }
            }
        }
        if (found) {
            for (int i = pairsList.size() - 1; i >= 0; i--) {
                System.out.println(pairsList.get(i));
            }
        } else {
            System.out.println("No valid pairs found");
        }
    }
}