Apache POI+Excel, how to split into parts?

Question

Java

Good afternoon. I am writing a program, the essence is this:
There is a large XLS file with a single sheet. It has a lot of data on it.
It is required to cut it into pieces (cut into pieces vertically).
The problem is this: When copying cells, styles, height, width, values ​​are transferred, but at the output we get a document without merged cells.
Here is the code to access all MergedRegions

for (int n = 0; n < sheet.getNumMergedRegions(); n++) {
                            CellRangeAddress mergedRegion = sheet.getMergedRegion(n);
                            // Just add it to the sheet on the new workbook.
                            sheet_out.addMergedRegion(mergedRegion);

How to select only those between lines m and n and apply them in the new document, given the line shift?