input: def is_cheerful(s):
      """You are provided with a string s.
      The challenge is to verify whether the string is cheerful.
      A string is considered cheerful if it has a minimum length of 3 and no group of three consecutive characters are the same.
      For example:
      is_cheerful(a) => False
      is_cheerful(aa) => False
      is_cheerful(abcd) => True
      is_cheerful(aabb) => False
      is_cheerful(adb) => True
      is_cheerful(xyy) => False
      """
output:     
      if len(s) < 3:
          return False
      for i in range(len(s) - 2):
          if s[i] == s[i+1] == s[i+2]:
              return False
      return True
  