import sys
import math
x1, y1= map(int, input().split())
x2, y2= map(int, input().split())
de = pow((pow(x1-x2, 2) + pow(y1-y2, 2)), 0.5)
dm = abs(x1 - x2) + abs(y1 - y2)
print(abs(dm - de))