x = list(map(float, input().split())) y = list(map(float, input().split())) x1 = x[0] x2 = y[0] y2 = y[1] y1 = x[1] print(f'{((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1))**(1/2):.4f}')
