a=list(input().split())
b=list(input().split())
de=((int(a[0])-int(b[0]))**2+(int(a[1])-int(b[1]))**2)**0.5
dm=abs(int(a[0])-int(b[0]))+abs(int(a[1])-int(b[1]))
finall=abs(dm-de)
print(finall)