christmas.java

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int counter = 0;

        int[] array = new int[n + 1];

        for (int i = 0; i < n - 1; i++) {
            int x1 = sc.nextInt();
            int x2 = sc.nextInt();
            array[x2] = x1;
        }

        for (int a = 1; a <= n; a++) {
            for (int b = 1; b <= n; b++) {
                if (a == b) continue;
                for (int c = 1; c <= n; c++) {
                    if (c == a || c == b) continue;
                    for (int d = 1; d <= n; d++) {
                        if (d == a || d == b || d == c) continue;
                        for (int e = 1; e <= n; e++) {
                            if (e == a || e == b || e == c || e == d) continue;
                            for (int f = 1; f <= n; f++) {
                                if (f == a || f == b || f == c || f == d || f == e) continue;
                                for (int g = 1; g <= n; g++) {
                                    if (g == a || g == b || g == c || g == d || g == e || g == f) continue;
                                    if ((array[b] == a || array[a] == b) && (array[c] == b || array[b] == c) && (array[d] == b || array[b] == d) && (array[e] == b || array[b] == e) && (array[f] == d || array[d] == f) && (array[g] == d || array[d] == g)){
                                        counter++;
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
        System.out.println(counter);
    }
}