"""
wiki: https://en.wikipedia.org/wiki/Heterogram_(literature)#Isograms
"""


def is_isogram(string: str) -> bool:
 """
 An isogram is a word in which no letter is repeated.
 Examples of isograms are uncopyrightable and ambidextrously.
 >>> is_isogram('Uncopyrightable')
 True
 >>> is_isogram('allowance')
 False
 >>> is_isogram('copy1')
 Traceback (most recent call last):
 ...
 ValueError: String must only contain alphabetic characters.
 """
 if not all(x.isalpha() for x in string):
 raise ValueError("String must only contain alphabetic characters.")

 letters = sorted(string.lower())
 return len(letters) == len(set(letters))


if __name__ == "__main__":
 input_str = input("Enter a string ").strip()

 isogram = is_isogram(input_str)
 print(f"{input_str} is {'an' if isogram else 'not an'} isogram.")