  In the Knill-Laflamme-Milburn (KLM) scheme, the success probability of
quantum teleportation is given by ${n \over n+1}$, wehre $2n$ is the number of
the ancilla qubits. For the high-fidelity approach in the KLM scheme, the
success probability is approximately given by $1-{1 \over n^{2}}$ for large
$n$. We give an explicit prescription to prepare an optimal ancilla state and
give an exact lower bound of the success probability for the high-fidelity
approach for arbitrary $n$.
