def is_integer(string: str) -> bool:
    """
    This function will check if a string (text) is an integer.
    So we only allow values such as:
    - 1
    - 1.0
    - 100

    But we never allows
    - 1.2
    - 45.221
    - Fiftyfive
    """
    try:
        f = float(string)
    except ValueError:
        return False

    if f.is_integer():
        return True
    else:
        return False

def get_mark(message: str):
    """
    This function will check if the input is correctly formatted
    and if not will repeat the input.
    It will only accepts integers.
    """
    while(True):
        s = input(message)
        if not is_integer(s):
            print("The input you have given is not valid Mark. Only input numbers. Please try again.")
            continue
        mark = int(float(s))
        if mark < 0 or mark > 100:
            print("A mark can not be smaller than 0 or bigger than 100. Please try again.")
            continue
        # The mark is correctly formatted. We return it.
        return mark



print("Welcome to Marks percentage calculator")
print("Here you will be able to find percentage of 5 subjects")
print("please enter your marks out of 100")

subjects = [
    "Science",
    "Maths",
    "Social Science",
    "English",
    "Computer",
]

marks = []
for subject in subjects:
    message = "Enter Your Marks in {}:".format(subject)
    mark = get_mark(message)
    marks.append(mark)

f = sum(marks) / len(marks) / 100
o = f * 100

print("Your Percentage in 5 subjects is", o)

p = 35
if o>=p:
   print("congratulations!")
else:
   print("Better luck next time")