  The Erd\H{o}s--Gallai Theorem states that for $k \geq 3$, any $n$-vertex
graph with no cycle of length at least $k$ has at most $\frac{1}{2}(k-1)(n-1)$
edges. A stronger version of the Erd\H{o}s--Gallai Theorem was given by
Kopylov: If $G$ is a 2-connected $n$-vertex graph with no cycle of length at
least $k$, then $e(G) \leq \max\{h(n,k,2),h(n,k,\lfloor
\frac{k-1}{2}\rfloor)\}$, where $h(n,k,a) := {k - a \choose 2} + a(n - k + a)$.
Furthermore, Kopylov presented the two possible extremal graphs, one with
$h(n,k,2)$ edges and one with $h(n,k,\lfloor \frac{k-1}{2}\rfloor)$ edges.
  In this paper, we complete a stability theorem which strengthens Kopylov's
result. In particular, we show that for $k \geq 3$ odd and all $n \geq k$,
every $n$-vertex $2$-connected graph $G$ with no cycle of length at least $k$
is a subgraph of one of the two extremal graphs or $e(G) \leq
\max\{h(n,k,3),h(n,k,\frac{k-3}{2})\}$. The upper bound for $e(G)$ here is
tight.
