BAEKJOON 2458 플로이드 와샬

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.StringTokenizer;

public class Main {
	static int N, M, ans;
	static int[][] map1, map2; 
	static boolean[] visit;
	static int[] number;
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer(br.readLine());
		N = Integer.parseInt(st.nextToken());
		M = Integer.parseInt(st.nextToken());
		map1 = new int[N+1][N+1];
		map2 = new int[N+1][N+1]; 
		number = new int[N+1];
		for (int i = 1; i <= N ; i++) {
			for (int j = 1; j <= N; j++) {
				if(i==j) 
					continue;
				map1[i][j] = 250000;
				map2[i][j] = 250000;
			}
		}
		for (int i = 0; i < M; i++) {
			st = new StringTokenizer(br.readLine());
			int s = Integer.parseInt(st.nextToken());
			int e = Integer.parseInt(st.nextToken());
			map1[s][e] = 1;
			map2[e][s] = 1;
		}
		for (int k = 1; k <=N; k++) {
			for (int i = 1; i <=N; i++) {
				if(k==i)continue;
				for (int j = 1; j <=N; j++) {
					if(k==j || i==j)continue;
					map1[i][j] = Math.min(map1[i][j], map1[i][k]+map1[k][j]);
					map2[i][j] = Math.min(map2[i][j], map2[i][k]+map2[k][j]);
				}
			}
		}
		for (int i = 1; i <= N ; i++) {
			for (int j = 1; j <= N; j++) {
				if(map1[i][j] != 0 && map1[i][j] < 250000)
					number[i]++;
				if(map2[i][j] != 0 && map2[i][j] < 250000)
					number[i]++;
			}
		}
		for (int i = 1; i <=N; i++) {
			if(number[i] == N-1)
				ans++;
		}
		System.out.println(ans);
	}
}