Что не так с кодом? - Pascal ABC (12785)

const n=3;                                                                    
var                                                                           
b:array[1..n] of real;                                                        
    f,s,i:real;                                                                   
                                                                    
    begin                                                                     
    writeln('vvod elementov');                                               
    for i:=1 to n do                                                          
    readln(b[i]);                                                             
    s:=0;                                                                     
    for i:=1 to n do                                                          
    begin                                                                     
    if b[i] mod 3=0 then f:=sqr(b[i])                                         
    else  if b[i] mod 3=1  then f:=b[i]                                       
    else f:=b[i]/3;                                                           
    s:=s+f;                                                                   
    end;                                                                      
    writeln('cyma',s:2:2);                                                    
    end.