import math
class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y


    def distance_between_points(self, p1, p2):
        delta_x = p2.x - p1.x
        delta_y = p2.y - p1.y
        return math.sqrt(delta_x ** 2 + delta_y ** 2)
        print(f'{distance:.3f}')

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

distance = Point(p1, p2)
distance.distance_between_points(p1,p2)