n,m,x,y=io.read("*n","*n","*n","*n")
x,y,f=x-1,y-1,math.floor
xm,ym=f(x/m),f(y/m)
xpm,ypm=x%m,y%m
xs=xm%2==1 and m-1-xpm or xpm
ys=ym%2==1 and m-1-ypm or ypm
print(xs==ys and "YES" or "NO")