PROGRAM SumNums;
VAR num:INTEGER;

   FUNCTION sumupto(n:INTEGER):INTEGER;
   VAR m:INTEGER;
   BEGIN
      sumupto:=0;
      IF n>0 THEN BEGIN
         m:=n-1;
         sumupto:=n+sumupto(m);
      END;
   END;

BEGIN
   GET(num);
   PUT(sumupto(num));
END.