# upper or lowercase allowed 

user_input = input()

if user_input.isalpha():
    print("Yes")
else: 
    print("No")


# if you want to check upper or lower (logic version)

user_input = input()

if user_input.isupper() or user_input.islower():
    print("Yes")
else:
    print("No")

#Which one to use? 

# any letters, any case = isalpha()
# only lowercase = islower()

# only uppercase = isupper()

#Upper or lower, but not mixed = isupper() or islower()