Your question is Coding With Conditional Logic. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Write pseudo-code that, given three integers (a, b, c), returns their sum. However, if any two of the variables are equal, don't include one (i.e., if a==b, return a+c or b+c but not a+b+c).