class Solution:

     def isValid(self, S: str) -> bool:

         n = len(S)

         if n % 3 != 0:

             return False

         while n!=0:

             i = S.find('abc')

             if i == -1:

                 return False

             else:

                 S = S[0:i] + S[i+3:]

                 n = len(S)

         return True