var
S,ans:string;
flag,l,r,p:longint;
begin
flag:=0;
read(S);
p:=0;
r:=Length(S)-1;
ans:=' ';
for  l:=p to r do
        begin
        if flag=1 then
        begin
            ans:=S[l]+ans;
            p:=p+1;
            flag:=0;
        end;
        if flag=0 then
        begin
            ans:=S[r]+ans; 
            r:=r-1;
            flag:=1;
        end;
    write(ans);
end.

说结尾错

Free Pascal Compiler version 3.0.4+dfsg-22 [2019/01/24] for x86_64

Copyright (c) 1993-2017 by Florian Klaempfl and others

Target OS: Linux for x86-64

Compiling /tmp/compiler_aponbixf/src

src(25,4) Fatal: Syntax error, ";" expected but "." found

Fatal: Compilation aborted

Error: /usr/bin/ppcx64 returned an error exitcode