Description

Original Source: USACO 2003 Fall

Every cow's dream is to become the most popular cow. Now there are $N$ cows, and you are given $M$ pairs of integers $(A,B)$, indicating that cow $A$ considers cow $B$ popular. This relationship is transitive—if cow $A$ considers cow $B$ popular, and cow $B$ considers cow $C$ popular, then cow $A$ also considers cow $C$ popular. Your task is to determine how many cows are considered popular by every other cow except themselves.

Input Format

The first line contains two numbers, $N$ and $M$;
The next $M$ lines each contain two numbers, $A$ and $B$, meaning cow $A$ considers cow $B$ popular (the given information may contain duplicates, meaning multiple occurrences of the same $A,B$ pair are possible).

Output Format

Output the number of cows that are considered popular by every other cow except themselves.

Sample 1

Only the third cow is considered popular by every other cow except itself.

3 3
1 2
2 1
2 3

1

Data Range and Hints

For all data, $1\le N\le 10^4,1\le M\le 5\times 10^4$.