Merge cells in an excel sheet by C#

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C#

.NET

C#3.5

I want to merge cells in an excel sheet using C#.
I am using this::

xlWorkSheet.Range[xlWorkSheet.Cells[1, 1], xlWorkSheet.Cells[1, 4]].Merge();

But When I use this, only the value that is present in the cell[1,1] is being saved in the excel but all the values in the cell [1,2],[1,3],[1,4] is removed.
How can I keep all the values from those four cells in one cell while merging?