Automatic Way of Writing Cumulative Sum Formula

Dear Experts,

Please have a look at my spreadsheet.

What do I want to do?

Given data in column A is just a small example. Like this, I have data in thousands of rows. In column C, I am writing a formula for the cumulative sum of the values that I will put in column B. Usually, I write the formula manually but is there any way that I can do in short period of time. thanks