Mbpp/797

def sum_in_range(l: int, r: int) -> int:
    """
    Returns the sum of all odd natural numbers in the inclusive range [l, r].
    Natural numbers are assumed to be positive integers (>=1), but the function
    works for any integer range.
    """
    # If the range is invalid (l > r), return 0.
    if l > r:
        return 0
    
    # Adjust l to the first odd number in the range.
    if l % 2 == 0:
        l += 1
    
    # Adjust r to the last odd number in the range.
    if r % 2 == 0:
        r -= 1
    
    # If after adjustment l > r, there are no odd numbers.
    if l > r:
        return 0
    
    # Number of odd numbers in the adjusted range.
    n = (r - l) // 2 + 1
    
    # Sum of an arithmetic progression: n * (first + last) / 2.
    return n * (l + r) // 2

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