var
    n,i,j,so,dong,cot : longint;
    a : array[1..100,1..100] of longint;
    b : array[1..100] of longint;
begin
    readln(n);
    for i:=1 to n do
    begin
        for j:=1 to n do
            read(a[i,j]);
        readln;
    end;
    so := 0;
    cot := 1;
    dong := 1;
    repeat
        i := dong;
        j := cot;
        repeat
            so := so + 1;
            b[so] := a[i,j];
            i := i - 1;
            j := j + 1;
        until ((j>n) or (i=0));
        cot := 1;
        dong := dong + 1;
    until (dong>n);
    cot := 2;
    dong := n;
    repeat
        i := dong;
        j := cot;
        repeat
            so := so + 1;
            b[so] := a[i,j];
            i := i - 1;
            j := j + 1;
        until ((j>n) or (i=0));
        dong := n;
        cot := cot + 1;
    until (cot>n);
    for i:=1 to so do
    begin
        write(b[i],' ');
    end;
end.

I couldn't understand why it is incorrect ? :(

Try the following test:

1
1

Your program's output is '1 0', but the correct one is obviously '1'.

P.S. Your code is unforgettable :)

Thanks :)

>> P.S. Your code is unforgettable :)

Why ? :)