#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;
const int N = 510;
int n, m;
int g[N][N];

// 匈牙利
int match[N], st[N];
int dfs(int u) {
    for (int i = 1; i <= n; i++)
        if (g[u][i] && !st[i]) {
            st[i] = 1;
            if (match[i] == -1 | dfs(match[i])) {
                match[i] = u;
                return 1;
            }
        }
    return 0;
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("POJ2594.in", "r", stdin);
#endif
    while (scanf("%d%d", &n, &m) && (n + m)) {
        memset(g, 0, sizeof g);
        while (m--) {
            int x, y;
            scanf("%d%d", &x, &y);
            g[x][y] = 1;
        }

        // Floyd传递闭包
        for (int k = 1; k <= n; ++k)
            for (int i = 1; i <= n; ++i)
                for (int j = 1; j <= n; ++j)
                    g[i][j] |= g[i][k] & g[k][j];

        int res = 0;
        memset(match, -1, sizeof match);
        for (int i = 1; i <= n; i++) {
            memset(st, 0, sizeof st);
            if (dfs(i)) res++;
        }

        printf("%d\n", n - res);
    }
    return 0;
}