function dech (s:string;k:integer):string;
var i,asciinr:integer;
begin
  i:=1;
  while s[i]<>#0 do
    begin
      asciinr:=(ord(s[i]));
        if (asciinr>97) and (asciinr<122) then
          begin
            asciinr:=asciinr-k;
            result[i]:=chr(asciinr);
          end;
        i:=i+1;
      end;
end;