What is the error in the code?

    aa=input('image.jpg');
    z=aa;
    e=input ('Enter lower threshold value ');
    f=input ('Enter higher threshold value ');
    %Grey level with background
    mask = (z>e) & (z<f);
    z(mask)=255;
    subplot(2,2,3);
    imshow(z);
    title ('Grey level sliced image with background');
    %Grey level without background
    mask = (z>e) & (z<f);
    z(mask)=255;
    mask1=(z<e) & (z>f);
    z(mask1)=0;
    subplot(2,2,4);
    imshow(z);
    title ('Grey level sliced image without background');

[Aquatris]

What error did you get?