Couple Ring Match

Interview

Time limit1sMemory limit1024 MB

Summary

Find every ring feature worn by exactly two people and print those pairs of names, ignoring anyone whose feature is '-'.

Level: Easy3 of 10
Topics: Hash map, Implementation
Solved: No attempts yet

Problem

Jonghyeon wants to find out how many couples there are at his school. Couples wear a distinctive ring on their left ring finger as a couple ring. After noticing this, Jonghyeon decided to check the left ring finger of every enrolled student. If exactly two people wear rings with the same feature, Jonghyeon considers those two a suspected couple. For the given input, find the people Jonghyeon considers suspected couples.

Input

The first line contains $N$ , the number of people whose left ring finger Jonghyeon checks. ( $1 \le N \le 1\,000$ ) Each of the next $N$ lines contains a person's name $p_i$ and the feature of their ring $s_i$ , separated by a space. If the person is not wearing a ring, $s_i$ is given as -. Both $p_i$ and $s_i$ are strings of length at most 50. All names $p_i$ are distinct. All names and ring features consist of English letters, digits, and underscores (_).

Output

On the first line, print the number of suspected couple pairs. If there is at least one pair, print each pair on its own line starting from the second line, with the two names separated by a space. The order does not matter.

Examples2

Example 1

Input

6
jonghyeon -
minkyu twisted_silver_matte
hyegeun thin_plated_gold
somin text_engraved_light_blue
daeun twisted_silver_matte
jiyoung thin_plated_gold

Expected output

2
minkyu daeun
hyegeun jiyoung

Example 2

Input

6
eardrum_buster motdoen_goyangi
ksap motdoen_goyangi
beenzino chanel
bongjunho chanel
poison motdoen_goyangi
bts chanel

Expected output