# from math import sqrt
# x1, y1=map(float,input().split())
# x2, y2=map(float,input().split())
# d=sqrt((x1-x2)**2+(y1-y2)**2)
# print("{:.4f}".format(d))

x1, y1=map(float,input().split())
x2, y2=map(float,input().split())
d=((x1-x2)**2+(y1-y2)**2)**0.5
print("{:.4f}".format(d))