**Input:** Two qubits (stored in an array of length 2) which are guaranteed to be in either the $\ket{00}$ or the $\ket{11}$ state.

**Output:** 0 if the qubits were in the $\ket{00}$ state, or 1 if they were in the $\ket{11}$ state. The state of the qubits at the end of the operation does not matter.
