Mutual Followers

You are given a two-dimensional list of integers relations. Each element relations[i] contains [a, b] meaning that person a is following person b on Twitter.

Return the list of people who follow someone that follows them back, sorted in ascending order.

Constraints

• 0 ≤ n ≤ 100,000 where n is the length of relations

https://binarysearch.com/problems/Mutual-Followers

Examples

Example 1

Input

• relations =

[[0,1],
 [2,3],
 [3,4],
 [1,0]]

Output

• answer = [0, 1]

Explanation

0 follows 1 and 1 follows 0.

Example 2

Input

• relations =

[[0,1],
 [1,2],
 [2,3],
 [3,0]]

Output

• answer = []

Explanation

There aren’t any mutual followers.

Solution