CF501B Misha and Changing Handles

Misha hacked the Codeforces site. Then he decided to let all the users change their handles. A user can now change his handle any number of times. But each new handle must not be equal to any handle that is already used or that was used at some point. Misha has a list of handle change requests. After completing the requests he wants to understand the relation between the original and the new handles of the users. Help him to do that.

The first line contains integer $ q $ ( $ 1

In the first line output the integer $ n $ — the number of users that changed their handles at least once. In the next $ n $ lines print the mapping between the old and the new handles of the users. Each of them must contain two strings, $ old $ and $ new $ , separated by a space, meaning that before the user had handle $ old $ , and after all the requests are completed, his handle is $ new $ . You may output lines in any order. Each user who changes the handle must occur exactly once in this description.