# Distance between two points

# -*- coding: utf-8 -*-

pt1 = raw_input().split()
x1,y1 = map(float,pt1)

pt2 = raw_input().split()
x2,y2 = map(float,pt2)

d = ((x2-x1)**2+(y2-y1)**2)**0.5

print "%.4f" %d
