You are given a bunch of wooden sticks. Each endpoint of each stick is colored with some color. Is it possible to align the sticks in a straight line such that the colors of the endpoints that touch are of the same color?
输入解释
Input is a sequence of lines, each line contains two words, separated by spaces, giving the colors of the endpoints of one stick. A word is a sequence of lowercase letters no longer than 10 characters. There is no more than 250000 sticks.
输出解释
If the sticks can be aligned in the desired way, output a single line saying Possible, otherwise output Impossible.
输入样例
blue red
red violet
cyan blue
blue magenta
magenta cyan