import math 
x1,y1=map(int,input().split())
x2,y2=map(int,input().split())
d_e=math.sqrt(math.pow((x1-x2),2)+math.pow((y1-y2),2))  	 # math.pow(x,y)用来计算x的y次方
d_m=abs(x1-x2)+abs(y1-y2)									 # abs函数用来计算绝对值
delta=abs(d_e-d_m)
print(delta)