def frequencies(ciphertext):
	freq=[0]*26
	for i in ciphertext:
		int_letter = ord(i) - ord('a')
		freq[int_letter]+=1
	return freq

def index(freq, cipher_length):
	sum =0
	i = 0
	while(i<=25):
		sum = sum + freq[i]*(freq[i]-1)
		i+=1
	denominator=cipher_length*(cipher_length-1)
	return float(sum)/(denominator)

def key_length(c_index, c_l):
	k = (0.0265*c_l)/((0.065-c_index)+c_l*(c_index-0.0385))
	return k

def main():

	ciphertextInput = input("input ciphertext ")
	ciphertextInput = ciphertextInput.replace(" ", "")
	ciphertextInput = ciphertextInput.replace("\t", "")
	ciphertextInput = ciphertextInput.replace(",", "")
	ciphertextInput = ciphertextInput.replace(";", "")
	ciphertextInput = ciphertextInput.replace("!", "")
	ciphertextInput = ciphertextInput.replace(":", "")
	ciphertextInputNoSpaces = ciphertextInput.replace(".", "")	
	print("after removing all whitespaces and punctuations")
	print(ciphertextInputNoSpaces)
	ciphertext = ciphertextInputNoSpaces.lower()
	print("after transferring to lowercase letters only")
	print(ciphertext)
	cipher_length = len(ciphertext)
	print("cipher length is ")
	print(cipher_length)

	freq = frequencies(ciphertext)
	print("frequencies are ")
	print(freq)
	
	c_index=index(freq, cipher_length)
	print("index of coincindence is")
	print(c_index)

	print("key length ")
	print(key_length(c_index, cipher_length))
main()