# 2024. Cow Contest

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

### 输入格式

• Line 1: Two space-separated integers: N and M

• Lines 2..M+1: Each line contains two space-separated integers that describe the competitors and results (the first integer, A, is the winner) of a single round of competition: A and B

### 输出格式

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

### 样例

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

Output
2
OUTPUT DETAILS:
Cow 2 loses to cows 1, 3, and 4. Thus, cow 2 is no better than any of the cows 1, 3, and 4. Cow 5 loses to cow 2, so cow 2 is better than cow 5. Thus, cow 2 must be fourth, and cow 5 must be fifth.The ranks of the other cows cannot be determined.


34 人解决，49 人已尝试。

45 份提交通过，共有 84 份提交。

4.1 EMB 奖励。