from math import sqrt


def almostEqual(x: float, y: float) -> bool:
    return abs(x - y) < 10**-9


def nthFibonacciNumber(n: int) -> float:
    """Return the nth Fibonacci number."""
    n += 1
    return ((1 + sqrt(5)) ** n - (1 - sqrt(5)) ** n) / (sqrt(5) * 2**n)


print("Testing nthFibonacciNumber()...", end="")
assert almostEqual(nthFibonacciNumber(0), 1)
assert almostEqual(nthFibonacciNumber(1), 1)
assert almostEqual(nthFibonacciNumber(2), 2)
assert almostEqual(nthFibonacciNumber(3), 3)
assert almostEqual(nthFibonacciNumber(4), 5)
assert almostEqual(nthFibonacciNumber(5), 8)

print("Passed!")