Temperature Converter (for all temperatures)

Code:
#Credits:

#Nevets04(I can't even count how much of his contributions helped me learn)

#Mr.FeellingLeSS(For the script that clears the shell for XP and Vista)

#Me?



import os

import platform



def clearer():

    systemver=platform.release()

    if systemver=='XP':

        os.system("cls")

    elif systemver=='Vista':

        os.system("clear")

    else:

        os.system("clear")

clearer()



print '***************************** *'

print '*         Welcome!                             '

print '*     To the uber1337                        '

print '*   Temperature Converter                 '

print '******************************'

raw_input('Press Enter to continue')

clearer()

print 'For Farenheit to Celsius, Press:1'

print  'For Farenheit to Kelvin, Press:2'

print 'For Celsius to Farenheit, Press:3'

print    'For Celsius to Kelvin, Press:4'

print    'For Kelvin to Celsius, Press:5'

print  'For Kelvin to Farenheit, Press:6'

x = input('What is it that you want to convert?:')

clearer()

def choice():

    if x==1:

        a = input('Enter your degrees Farenheit here:')

        print (a - 32) * 5/9

    if x==2:

        b = input('Enter your degrees Farenheit here:')

        print (b - 32) * 5/9 + 273

    if x==3:

        c = input('Enter your degrees Celsius here:')

        print c * 9/5 + 32

    if x==4:

        d = input('Enter your degrees Celsius here:')

        print d + 273

    if x==5:

        e = input('Enter your degrees Kelvin here:')

        print e - 273

    if x==6:

        f = input('Enter your degrees Kelvin here:')

        print (f - 273) * 9/5 + 32

choice()

raw_input()