How would I design a simple logic circuit for 3 input bits?
We normally present this kind of requirement in a truth table.
I'll assume that for the input combinations you didn't specify in the question, you don't care what the output is. In the truth table, we'll represent this with an "X".
Then you have a truth table like this:

IN2  IN1  IN0  |  OUT
---------------------
 0    0    0   |   X
 0    0    1   |   X
 0    1    0   |   1
 0    1    1   |   0
 1    0    0   |   0
 1    0    1   |   1 
 1    1    0   |   X
 1    1    1   |   X


You can easily realize this truth table by simply XOR'ing bits 0 and 1, and ignoring bit 2.