Hi

To get a seat in IIT Madras in Computer Science, you need to meet the cutoff of the institute. The cutoff is the minimum marks required for admission. This means that if you score less than the minimum marks (or cutoff), you will have less chances of getting admission. The cutoff varies from branch to branch, college to college and category to category. 

You can refer to the link given below to check the previous year cutoff of IIT Madras and estimate it for this year. It might fluctuate a little bit.

https://engineering.careers360.com/articles/jee-advanced-cutoff-for-iit-madras

Hope this helps!

All the best !