def print_execution_time(day, part, avg_time):
    units = ['s', 'ms', 'μs', 'ns']
    unit = 0
    while avg_time < 1:
        avg_time *= 1000
        unit += 1

    print("Average execution time for day %s part %s: %1.2f%s" % (day, part, avg_time, units[unit]))