  We show that for any nontrivial knot $K$ and any natural number $n$ there is
a diagram $D$ of $K$ such that the unknotting number of $D$ is greater than or
equal to $n$. It is well known that twice the unknotting number of $K$ is less
than or equal to the crossing number of $K$ minus one. We show that the
equality holds only when $K$ is a $(2,p)$-torus knot.
