There are several test cases, you should process to the end of file.For each test case, there are two numbers n m on the first line, indicates the number processes and the number of dependencies. $1 \leq n \leq 100, 1 \leq m \leq 10000$The next following m lines, each line contains two numbers a b, indicates a dependencies (a, b). $1 \leq a, b \leq n$
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