Intermediate vertices X34137

Given a directed graph and two different vertices $u$ and $v$, compute how many vertices $x$ different from $u$ and $v$ there are such that there exists some path from $u$ to $v$ passing through $x$.

Input

The input consists in several cases. Each case begins with $n$, $u$, $v$ and $m$, followed by $m$ different pairs $x$ $y$, with $x \neq y$, which indicate an arc that goes from $x$ to $y$. Assume $2 \leq n \leq 10^4$, $0 \leq m \leq 10n$, and that the vertices are numbered between $0$ and $n - 1$.

Output

For each case, write the number of vertices that can be visited when going from $u$ to $v$ following some path.

Hint

For each case, essentially the expected solution only makes two traversals, each on the right graph.