2024. Cow Contest

单点时限: 2.0 sec

内存限制: 256 MB

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.

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.

33 人解决,48 人已尝试。

44 份提交通过,共有 83 份提交。

4.2 EMB 奖励。

创建: 12 年,10 月前.

修改: 3 年,3 月前.

最后提交: 4 天,22 小时前.

来源: USACO

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