#208.py
tx,ty = input().split()
hx,hy = input().split()
tx,ty = int(tx),int(ty)
hx,hy = int(hx),int(hy)
x,y = 0,0
lx,ly = -1,-1
c = 0


lx = tx-x
ly = ty-y
if(lx == ly):
    if(hx-hy == 0):
        if(hx>tx):
            c=tx
        else:
            c=tx+1
    else:
        c=tx
if(lx < ly):
    c=ly
if(lx > ly):
    c=lx
print(c)