Fibonacci

decl
    int n,f2,f0,f1,i;
enddecl
read(n);
if(n>=2) then
    f0=0;
    f1=1;
    n=n-1;
    while(n!=0) do
        f2=f1+f0;
        f0=f1;
        f1=f2;
        n=n-1;
    endwhile;
    write(f1);
else if(n==1) then
        write(1);
    else write(0);
    endif;
endif;