学步园

#include<iostream>
#include<cstring>
#include<cstdio>
#define inf 0x7fffffff
using namespace std;

inline int read() {
    int x = 0, f = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
        if (ch == '-')f = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
        x = x * 10 + ch - '0';
        ch = getchar();
    }
    return x*f;
}

int n, m, ans;
bool a[101][101];

int main() {
    n = read();
    m = read();
    for (int i = 1; i <= m; i++) {
        int x = read(), y = read();
        a[x][y] = 1;
    }
    for (int k = 1; k <= n; k++)
        for (int i = 1; i <= n; i++)
            for (int j = 1; j <= n; j++)
                a[i][j] = a[i][j] || (a[i][k] && a[k][j]);
    for (int i = 1; i <= n; i++) {
        int sum = 0;
        for (int j = 1; j <= n; j++)
            if (a[i][j] || a[j][i])sum++;
        if (sum == n - 1)ans++;
    }
    printf("%d", ans);
    return 0;
}