tx,ty = input().split()
hx,hy = input().split()

tx,ty = int(tx),int(ty)
hx,hy = int(hx),int(hy)
x,y = 0,0
#x_,y_ = 0,0
lx,ly = 0,0
c = 0
pt = 0

while (tx != x)&(ty != y):
    c += 1
    lx = tx-x
    ly = ty-y
    if (lx==ly):
        pt = 1
        x,y = x+1,y+1
    if (lx> ly):
        pt = 2
        x += 1
    if (lx< ly):
        pt = 3
        y += 1
    if (x == hx)&(y == hy):
        if (pt == 1):
            x-=1
        if (pt == 2):
            y+=1
        if (pt == 3):
            x+=1
    #x_,y_ = x,y
print(c)