p1 = input()
p1 = p1.split(' ')
p2 = input()
p2 = p2.split(' ')

x1 = float(p1[0])
y1 = float(p1[1])
x2 = float(p2[0])
y2 = float(p2[1])

calc = (((x2 - x1)**2 + (y2 - y1)**2)**(1/2))

print('{:.4f}'.format(calc))