I wrote a program for 1068 "Sum" - the code is really very
easy. Judge program says always me "wrong answer". Where is
my mistake? Could anybody help me?

program p;
var i,n:longint;
    res:longint;
begin
  read(n);
  res := 0;
  if (n >=1) then
     for i:=1 to n do res := res + i
  else
     for i:=1 downto n do res := res + i;
  write(res);
end.

I just took your solution and changed loop downto a little.
This will be accepted: (has already been:).
Mind that you don't have to use loop at all - just using
formula n*(n+1)/2 seperately for n>=1 and n<1 :)
I can post my solution here if you want, or send it by email

program p;
var i,n:longint;
    res:longint;
begin
  read(n);
  res := 0;
  if (n >=1) then
     for i:=1 to n do res := res + i
  else begin
     res:=1;
     for i:=1 to -n do res := res - i;
  end;
  write(res);
end.