import math

p1 = input().split()
x1 = float(p1[0])
y1 = float(p1[1])

p2 = input().split()
x2 = float(p2[0])
y2 = float(p2[1])

distancia = math.sqrt((x2-x1) ** 2 +(y2-y1) ** 2)
print("%.4f" % distancia)