Cow Contest

$N$ ($1 \le N \le 100$) cows, conveniently numbered $1$ through $N$, are competing in a programming contest. As everyone knows, some cows code better than others. Each cow has a fixed skill rating that is unique among the competitors.

The contest is run as a series of head-to-head rounds, each between two cows. If cow $A$ has a higher skill level than cow $B$ ($1 \le A \le N$, $1 \le B \le N$, $A \ne B$), then cow $A$ always beats cow $B$.

Farmer John wants to rank the cows by skill. Given the results of $M$ ($1 \le M \le 4500$) two-cow rounds, determine how many cows have a rank that can be precisely determined from those results. The round results are guaranteed to be free of contradictions.

• Line 1: Two space-separated integers, $N$ and $M$.
• Lines $2$ through $M+1$: Each line contains two space-separated integers describing one round, $A$ and $B$, where the first integer $A$ is the winner.

• Line 1: A single integer, the number of cows whose rank can be determined.