Need to reference the value of a third column when searching a range for a specific value

I have a large amount of data (50,000 rows or so), and for the sake of my question there are 3 relevant columns; column A that contains a program number, column B that contains a task number (there are many tasks that will have the same program number), and column C that contains task numbers that have met a series of other requirements (all these task numbers exist in column B). I'm trying to write a function that when i search column B with a specific value from column C, it will give me the value of column A where column B is equal to that value from column C.
Example:

Column A...........Column B............Column C
Program#....... Task#..............Important task#.........Output that i want
1...................... A ......................... B................................1
1...................... B ......................... E................................2
1......................C .........................H..................................3
2......................D .........................J ..................................3
2...................... E .........................M................................ 4
2......................F
2...................... G
3...................... H
3...................... I
3...................... J
4...................... K
4...................... L
4...................... M

I understand the concepts of writing functions and I've tried tinkering with making an IF function work, but I don't have a big enough knowledge base of them and I just can't seem to figure out how to make this work or if it's even possible. I'm open to any sort of solution that will accomplish the end goal. Thanks!

welcome to the forum, carterbu. maybe:
=INDEX(A:A,MATCH(C2,B:B,0))

if it doesn't work, I suggest you upload an Excel file in the thread. To do that, Click on GO ADVANCED and use the paperclip icon to open the upload window.
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and to illustrate your example better, click on How To Get Quick & Good Answers

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