# string = "aabc"
# string+= " "
# index = len(string)-1
# for i in range(len(string)):
#     for j in range(i+1,len(string)):
#         if (~ord(string[j])) == ~ord(string[i]):
#             if string[i] not in string[index:]:
#                 string+=string[i]
#                 print(string[i],end="")
