input: Write a python function to check if a string contains any 4-letter palindromes.
  assert is_palindrome("abccba") == True
  assert is_palindrome("abcdedcba") == True
  assert is_palindrome("abcdefgh") == False
output: def is_palindrome(s):
      for i in range(len(s) - 3):
          if s[i] == s[i+3] and s[i+1] == s[i+2]:
              return True
      return False