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Because of the latest mishaps of their agents, Central Intelligence Agency of Byteland resolved to improve their activity. So far the biggest trouble has been a preparation of safe meetings of agents. Your program has to help in solving this. For a given description of the net of roads in Byteland and the initial positions of two agents, it should answer if their safe meeting is possible.
To consider a meeting safe the agents must hold to the following precautions:
Write a program which:
In the first line of the standard input, there are two integers and separated by a single space, where , .
In the second line there are two integers and separated by a single space, , and , denoting respectively the starting positions of agents No 1 and No 2.
In the following lines there are pairs of natural numbers and separated by single spaces, and , denoting that there is a road from city to city .
There should be exactly one line in the standard input and it should contain:
For the input data:
6 7 1 5 1 2 4 5 2 3 3 4 4 1 5 4 5 6
the correct result is:
Task author: Tomasz Walen.