IF function with ISBlank

Hello, 

Scenario: 
If A1 is blank, try to get data from B1. 
If B1 is blank as well, try to get data from C1

If A1 is not blank, continue to use the data from A1. 

I have =IF(ISBLANK(A1),B1,IF(ISBLANK(A1,C1,A1)) 

It's filling in my blanks from column A with column B where applicable, but when column C has a value it's not pulling in. Would love if someone could correct my forumla but also explain where I went wrong, as I'm trying to learn and better my syntax. Thanks in advance!!