Implementation if statement with two different conditions

I have a code using if and else with two different condition 1. if FS1 <= 1 else FS1>1 2. if depth < 20 else depth>20

This is detail of my code: LPi_all=[ ]; for i=1:length(FS1);

    depth_allD=[ ];
    if FS1 <= 1 
    for j=1:length(depth);
        if depth < 20        % F=1-Fs

            w=(10-0.5*depth(j))  

        else depth > 20

                w=0     

           LPi= (1-FS1(i))*w*3

        end  

    else FS1>1

            LPi= 0 

    end
end

 I have a wrong position in the placement the second else. 
Error: File: Input_RegLPI.m Line: 335 Column: 5
Illegal use of reserved keyword "else".

Is there any solution for my case

Thanks