Merge cells based on codition

[csl6989]

Hi
I am trying to merge cells with conditional formating.
I am trying to represent below but its hard. hope you guys understand what I need.

Ie:
1.I would like to merge From Jan1 to Jan 4 and write insde the merged cells "A"
2.Merge Jan 5th to Jan 9th and write inside the merged cells "B"
3.Merge Jan 10th to end and write inside the merged cells "C".
[TABLE="width: 1000"]
<TBODY>[TR]
[TD]Jan-1-2014
[/TD]
[TD]Jan-5-2014
[/TD]
[TD]Jan-10-14
[/TD]
[TD]Jan-1-2014
[/TD]
[TD]Jan-2-2014
[/TD]
[TD]Jan-3-2014
[/TD]
[TD]Jan-4-2014
[/TD]
[TD]Jan-5-2014
[/TD]
[TD]Jan-6-2014
[/TD]
[TD]Jan-7-2014
[/TD]
[TD]Jan-8-2014
[/TD]
[TD]Jan-9-2014
[/TD]
[TD]Jan-10-2014
[/TD]
[TD]Jan-11-2014
[/TD]
[TD]Jan-12-2014
[/TD]
[TD]Jan-13-2014
[/TD]
[TD]Jan-14-2014
[/TD]
[/TR]
[TR]
[TD]A
[/TD]
[TD]B
[/TD]
[TD]C
[/TD]
[TD]A[/TD]
[TD]A[/TD]
[TD]A[/TD]
[TD]A[/TD]
[TD]B[/TD]
[TD]B[/TD]
[TD]B[/TD]
[TD]B[/TD]
[TD]B[/TD]
[TD]C[/TD]
[TD]C[/TD]
[TD]C[/TD]
[TD]C[/TD]
[TD]C[/TD]
[/TR]
</TBODY>[/TABLE]

but instead of having A written multiple time, cells merged and A written once.
Thanks