Looking for a formula for filling the data upto certain number of rows

Hi all,

First of all i would like to thank all the members for giving a prompt response and providing a solution of my problem in a very short time.

This time i need your help again. I have a workbook with three sheets in it. I use to paste an amount of data, in the form of a table, in sheet 1 and sheet 2 but every time the number of rows are different. Now i match the data of both the sheets using index and match function, which i have applied in sheet 3 and is working fine. The problem is that if my data in sheet one is upto the 100 rows, i have to drag down the formula in sheet 3 upto 100 rows for getting desired result every time. So i am searching for a formula which can find the last row number of filled cell in sheet 1 and automatically fills the formula in sheet 3 up to that row number accordingly. If this is possible through VBA code i am ready to try this also.

Guys help me out. Thanx in advance.