Slope finder

import os
os.system("clear")
while True:
print "--------------------------------------------------"
print " Slope Finder "
print "--------------------------------------------------"
a = 0
b = 0
c = 0
d = c
a = input("First x: ")
b = input("First y: ")
c = input("Second x: ")
d = input("Second y: ")
print d - b,"/",c - a