# Cow Contest

Time Limit: 1000MS

Memory Limit: 65536K

## Description

*N* (1 ≤ *N* ≤ 100) cows, conveniently numbered 1..*N*, are participating in a programming contest. As we all know, some cows code better than others. Each cow has a certain constant skill rating that is unique among the competitors.The contest is conducted in several head-to-head rounds, each between two cows. If cow *A* has a greater skill level than cow *B* (1 ≤ *A* ≤ *N*; 1 ≤ *B* ≤ *N*; *A* ≠ *B*), then cow *A* will always beat cow *B*.Farmer John is trying to rank the cows by skill level. Given a list the results of *M* (1 ≤ *M* ≤ 4,500) two-cow rounds, determine the number of cows whose ranks can be precisely determined from the results. It is guaranteed that the results of the rounds will not be contradictory.

## Output

* Line 1: A single integer representing the number of cows whose ranks can be determined

## Source

USACO 2008 January Silver