Checking equality/inequality of multiple variables [closed]

Let's say we have four variables: int a, b, c, d;. I need to check if excatly two of them are equal.

So for example: 1 1 9 5 is true, but 3 9 8 4 and 3 3 3 1 are false.

Of course writing an if statement for this would take a lot of time, won't be easily readable and it would be easy to make a mistake writing it.

What is the best way to write such statement?