text: from math import sqrt
  
  p1 = input().split(" ")
  
  p2 = input().split(" ")
  
  x1, y1 = p1
  
  x2, y2 = p2
  
  distancia = sqrt((float(x2) - float(x1)) ** 2 + (float(y2) - float(y1)) ** 2)
  
  print("%.4f" %distancia)
  