Idoc - Seguemnt - Field value

Hi.
I receive a IDOC number and name of a segment type, and a field name.

How could i get the value of the specific Field

I have this to a seguement elknvvm:

DATA: LV_DOCNUM TYPE DOCNUM,
      lv_segfd     TYPE int_seg-fieldname.


select-OPTIONS: S_DOCNUM for LV_DOCNUM.

START-OF-SELECTION.

SELECT * FROM EDID4 INTO TABLE @DATA(LIT_EDID4) WHERE DOCNUM IN @S_DOCNUM.

SELECT-OPTIONS: s_segfd FOR lv_segfd NO INTERVALS.

READ TABLE LIT_EDID4 INTO DATA(LWA_EDID4) INDEX 3.

lwa_elknvvm = LWA_EDID4-SDATA.
LOOP AT S_SEGFD.

... do stuff if the value (put in excel document)

endloop.

How could i get the field, user inserted in the search screen, example WKURS?

Thanks in advance.