import math
x1,x2=map(int,input().split())
y1,y2=map(int,input().split())
x=max(x1,x2)-min(x1,x2)
y=max(y1,y2)-min(y1,y2)
print("%.3f"%math.sqrt(x*x+y*y))

AC测试点：#2，#4，#5，#8