from math import*

pontoAx = float(input("Digite ponto Ax: "))
pontoAy = float(input("Digite ponto Ay: "))
pontoBx = float(input("Digite ponto Bx: "))
pontoBy = float(input("Digite ponto By: "))

d = sqrt((pontoBx - pontoAx) ** 2))

print (round(d, 3))