def prt(x,y,x_2,y_2):
    if(x==0):
        print(abs(y))
    elif(y==0):
        print(abs(x))
    else:
        if(abs(x)==abs(y)):
            if(abs(x_2)==abs(y_2) and x*x_2>0 and y*y_2>0 and abs(x)>abs(x_2)):
                print(abs(x)+1)
            else:
                print(abs(x))
        else:
            print(abs(x)+abs(y)-min(abs(x),abs(y)))
            
x,y=list(map(int,input().split()))
x_2,y_2=list(map(int,input().split()))
prt(x,y,x_2,y_2)