x1, y1 = input().split(' ')
x2, y2 = input().split(' ')
x1 = float(x1)
x2 = float(x2)
y1 = float(y1)
y2 = float(y2)
dist = ((x2 - x1)**2) + ((y2 - y1)**2)
fim = dist** (1/2)
print('{:.4f}'.format(fim))
