LSB embeded using image steganography

Can you help me for understand this code (S)

x = imread(cover); % cover message

y = imread(message); % message image

n = input('Enter the no of LSB bits to be subsituted- ');

S = uint8(bitor(bitand(x,bitcmp(2^n-1,8)),bitshift(y,n-8))); %Stego

E = uint8(bitand(255,bitshift(S,8-n))); %Extracted

[yanqi liu]

yes，sir，what value should n set？such as 7、6、……