# ADA Training CP

# Cow Contest

n 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, 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 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.

## Input data

The first line contains two integers n (1 ≤ n ≤ 100) and m (1 ≤ m ≤ 4500). Each of the next m lines contains two integers that describe the competitors and results (the first integer a, is the winner) of a single round of competition: a and b.

## Output data

Print a single integer representing the number of cows whose ranks can be determined.

## Examples

5 5 4 3 4 2 3 2 1 2 2 5

2