#!/usr/bin/python

def caesar(phrase, shift):
    letters = 'abcdefghijklmnopqrstuvwxyz'
    trans = dict([(letters[i], letters[(i + shift) % 26]) for i in range(26)])
    outstring = ''

    for a in phrase:
        if trans.has_key(a.lower()):
            if a.islower():
                outstring += trans[a]
            else:
                outstring += trans[a.lower()].upper()
        else:
            outstring += a

    return outstring

def uncaesar(phrase, dictionary='/usr/share/dict/words'):
    likely = [0 for a in range(26)]

    for i in range(26):
        words = caesar(phrase, i).split()
        for word in words:
            for line in open(dictionary).readlines():
                if word.lower() == line.lower().strip():
                    likely[i] += 1
                    break
    
    shift, high = -1, -1
    for i in range(26):
        if likely[i] > high:
            shift = i
            high = likely[i]

    return caesar(phrase, shift)


phrase = raw_input("Phrase to encrypt? ")
shift = int(raw_input("Shift by? "))

shifted = caesar(phrase, shift)
print "Encrypted:", shifted

print "Decrypting..."
shifted = uncaesar(shifted)
print "Decrypted:", shifted

if shifted == phrase:
    print "Success!"
else:
    print "Fail!"