Am I stupid or what?
code seems to be working

var x,a,b:integer;
function sum(x:integer): INTEGER;
  var s:integer;
  begin
  while x>0 do
    begin
    s:=s+x mod 10;
    x:=x div 10;
    end;
  sum:=s;
  end;
begin
read (x);
a:=x div 1000;
b:=x mod 1000;
if (sum(a)=sum(b+1)) or (sum(a)=sum(b-1)) then writeln ('Yes')
else writeln ('No');
end.

Pay attention to inc and dec in your code.
You should do first x+1 and x-1.
I hope you understand  me