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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:


def fib(n: int):
    """Return n-th Fibonacci number. 55 1 21 """
    if n == 0:
        return 0
    if n == 1:
        return 1
    return fib(n - 1) + fib(n - 2)
