Data not getting printed in excel sheet after using formula

I am trying to use XSSFRow to use data from one sheet to other,here is the code

XSSFRow r = nfrntSheet.getRow(i);
Cell c = r.createCell(7);
c.setCellFormula("'Original'!F"+(i+1)+"+'Original'!G"+(i+1)+"*-1");

After computing the formula the data in the written sheet will be displaced like "#value" instead of the number. what should i do to so that original data is displayed instead of the "#value"