[Check-IO] Lightbulb Intro

Problem: py.checkio.org/en/mission/lightbulb-intro/
My solution

def sum_light(els: List[datetime]) -> int:
    """
        how long the light bulb has been turned on
    """
    time = 0 
    for n in range(len(els) // 2):
        time += (els[2 * n + 1] - els[2*n]).total_seconds()
    return int(time)