
    Design a function for an adaptive learning system that calculates the total learning value when presenting a student with progressively easier versions of the same problem. Starting from an initial difficulty level, the system creates simplified versions by reducing the difficulty by 2 points each time until reaching the easiest possible version (where difficulty becomes 0 or 1). The function should sum up the difficulty values of all versions created (including the initial level), representing the complete learning path from most challenging to most accessible. For example, with an initial difficulty of 6, the system would create versions at levels 6, 4, and 2, and the function should return their sum.
    

    
def sum_series(n):
    """
    Design a function for an adaptive learning system that calculates the total learning value when presenting a student with progressively easier versions of the same problem. Starting from an initial difficulty level, the system creates simplified versions by reducing the difficulty by 2 points each time until reaching the easiest possible version (where difficulty becomes 0 or 1). The function should sum up the difficulty values of all versions created (including the initial level), representing the complete learning path from most challenging to most accessible. For example, with an initial difficulty of 6, the system would create versions at levels 6, 4, and 2, and the function should return their sum.
    

    """
def sum_series(n):
    """
    Design a function for an adaptive learning system that calculates the total learning value when presenting a student with progressively easier versions of the same problem. Starting from an initial difficulty level, the system creates simplified versions by reducing the difficulty by 2 points each time until reaching the easiest possible version (where difficulty becomes 0 or 1). The function should sum up the difficulty values of all versions created (including the initial level), representing the complete learning path from most challenging to most accessible. For example, with an initial difficulty of 6, the system would create versions at levels 6, 4, and 2, and the function should return their sum.
    

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