Sum of reciprocal up to n

MODULE z;
FROM RealInOut IMPORT WriteReal;
FROM InOut IMPORT WriteString, WriteLn, WriteCard, ReadCard;
CONST
    dgr = 1;
    ggr = 1000;
TYPE
    INTERVAL = [dgr..ggr];
VAR
   sum : REAL;
   ok : BOOLEAN;
   n : CARDINAL;

PROCEDURE SOR(n: CARDINAL; VAR ok: BOOLEAN): REAL;
VAR
   sum : REAL;
   i : INTERVAL;
BEGIN
     IF (n > dgr) AND (n < ggr) THEN
       ok := TRUE;
       sum := 1.0;
       FOR i := 2 TO n DO
          sum := sum + (1.0/FLOAT(i))
       END;
       RETURN sum
     ELSE
         ok := FALSE;
         RETURN 0.0
     END;
END SOR;

BEGIN
     WriteString('Enter the range, n: ');
     ReadCard(n);
     WriteLn;
     sum := SOR(n,ok);
     IF ok THEN
       WriteString('Sum of reciprocal up to');
       WriteCard(n,0);
       WriteString(' is: ');
       WriteReal(sum,0)
     ELSE
       WriteString('n is not in RANGE, modifies it in CONST!');
       WriteLn
     END
END z.