def encrypt(s, n):
	result = ""
	for c in s.lower():
		if 'a' <= c and c <= 'z':
			nextValue = ord(c) + n
			if nextValue > ord('z'):
				# FIXME: what if n is much greater than 26?
				nextValue -= 26 
			result += chr(nextValue)
		else:
			result += c

	return result

# hmm... looks redundant compared to encrypt()
def decrypt(s, n): 
	result = ""
	for c in s.lower():
		if 'a' <= c and c <= 'z':
			nextValue = ord(c) - n
			if nextValue < ord('a'):
				# FIXME: what if n is much less than 26?
				nextValue += 26
			result += chr(nextValue)
		else:
			result += c

	return result

encode = raw_input("Encrypt or Decrypt? (E/D) ")
msg = raw_input("What is the message? ")
rot = input("How many rotations? ")

if encode == 'E': # requires precise input from user
	print "Here's the ciphertext:", encrypt(msg, rot)
elif encode.startswith('D'): # user can input "Decrypt" or "Don't do it!" but not "decrypt"
	print "Here's the plaintext:", decrypt(msg, rot)