B. Misha and Changing Handles
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output
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.
Input
The first line contains integerq(1≤q≤1000), the number of handle change requests.
Nextqlines contain the descriptions of the requests, one per line.
Each query consists of two non-empty stringsoldandnew, separated by a space. The strings consist of lowercase and uppercase Latin letters and digits. Stringsoldandneware distinct. The lengths of the strings do not exceed20.
The requests are given chronologically. In other words, by the moment of a query there is a single person with handleold, and handlenewis not used and has not been used by anyone.
Output
In the first line output the integern— the number of users that changed their handles at least once.
In the nextnlines print the mapping between the old and the new handles of the users. Each of them must contain two strings,oldandnew, separated by a space, meaning that before the user had handleold, and after all the requests are completed, his handle isnew. You may output lines in any order.
Each user who changes the handle must occur exactly once in this description.
Sample test(s)
input
5Misha ILoveCodeforcesVasya PetrovPetrov VasyaPetrov123ILoveCodeforces MikeMirzayanovPetya Ivanov
output
3Petya IvanovMisha MikeMirzayanovVasya VasyaPetrov123
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，家门前的那条小路，到底通向了什么样的远方呢？
