
    Design an algorithm for an adaptive learning system that calculates the total challenge score across multiple difficulty adjustments. Starting from an initial difficulty level, the system needs to sum up the scores as it progressively reduces the difficulty by 2 points at each step until reaching a baseline level (zero or below). For example, if starting at difficulty level 7, the system would calculate the sum of difficulties 7, 5, 3, and 1 to determine the overall learning path score. This calculation helps determine optimal starting points for new students by considering the cumulative challenge across all potential difficulty levels they might encounter.
    

    
def sum_series(n):
    """
    Design an algorithm for an adaptive learning system that calculates the total challenge score across multiple difficulty adjustments. Starting from an initial difficulty level, the system needs to sum up the scores as it progressively reduces the difficulty by 2 points at each step until reaching a baseline level (zero or below). For example, if starting at difficulty level 7, the system would calculate the sum of difficulties 7, 5, 3, and 1 to determine the overall learning path score. This calculation helps determine optimal starting points for new students by considering the cumulative challenge across all potential difficulty levels they might encounter.
    

    """
def sum_series(n):
    """
    Design an algorithm for an adaptive learning system that calculates the total challenge score across multiple difficulty adjustments. Starting from an initial difficulty level, the system needs to sum up the scores as it progressively reduces the difficulty by 2 points at each step until reaching a baseline level (zero or below). For example, if starting at difficulty level 7, the system would calculate the sum of difficulties 7, 5, 3, and 1 to determine the overall learning path score. This calculation helps determine optimal starting points for new students by considering the cumulative challenge across all potential difficulty levels they might encounter.
    

    """
    if n < 1:
        return 0
    else:
        return n + sum_series(n - 2)