def getClassNumberString(classNumber):
    """
    Get the formatted string filtered out 'F00..' in class code.
    >>> getClassCodeString("F001AH")
    ' 1AH'
    >>> getClassCodeString("F0010")
    '  10'
    >>> getClassCodeString("F248A")
    '248A'
    """

    # first generate the list of number 1 to 9 for later use.
    one_to_nine = [str(i) for i in range(1, 10)]
    num = 0

    # loop through classCode to find the first number in it
    for i in range(len(classNumber)):
        if classNumber[i] in one_to_nine:
            num = i
            break

    # get the target substring based on the num that we just got
    target = classNumber[num:]
    return (4 - len(target)) * " " + target