**Input**: Two qubits stored in an array which are guaranteed to be either in a superposition of the states $|++\rangle$ and $|--\rangle$ or in a superposition of states $|+-\rangle$ and $|-+\rangle$.

**Output**: 0 if qubits were in the first superposition, 1 if they were in the second superposition.  
The state of the qubits at the end of the operation should be the same as the starting state.
