# Periodic Fibonacci

Consider the construction of a new sequence $$S$$ by taking the Fibonacci sequence modulo 10.

The first few terms of $$S$$ are $$S = 0,1,1,2,3,5,8,3,1,4,5,9,\ldots$$.

Find the fundamental period of $$S$$.

If $$S$$ is not period, enter your answer as -1.

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