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"""
This module provides a function to calculate the nth Fibonacci number using an iterative approach.
"""
def fibonacci(n: int) -> int:
"""
Calculate the nth Fibonacci number.
The Fibonacci sequence is a series of numbers where each number is the sum of the two preceding ones.
Typically starting with 0 and 1.
Args:
n (int): The position in the Fibonacci sequence to calculate. Must be a non-negative integer.
Returns:
int: The nth Fibonacci number.
Raises:
ValueError: If n is not a non-negative integer.
"""
if not isinstance(n, int):
raise ValueError("Input must be an integer.")
if n < 0:
raise ValueError("Input must be a non-negative integer.")
if n == 0:
return 0
elif n == 1:
return 1
a, b = 0, 1
for _ in range(2, n + 1):
a, b = b, a + b
return b
if __name__ == "__main__":
# Example usage:
try:
position = 10
result = fibonacci(position)
print(f"The {position}th Fibonacci number is: {result}")
except ValueError as e:
print(f"Error: {e}")
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