#include <bits/stdc++.h>
using namespace std;
const int N = 210, M = 30010;
int n, m;
int g[N][N], st[N];
int match[N];

int dfs(int x) {
    for (int i = 1; i <= n; i++) {
        if (g[x][i] && !st[i]) {
            st[i] = 1;
            int t = match[i];
            if (t == -1 || dfs(t)) {
                match[i] = x;
                return 1;
            }
        }
    }
    return 0;
}

int main() {
    memset(match, -1, sizeof match);
    scanf("%d %d", &n, &m);

    while (m--) {
        int a, b;
        scanf("%d %d", &a, &b);
        g[a][b] = 1;
    }

    // floyd求传递闭包
    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;
    for (int i = 1; i <= n; i++) {
        memset(st, 0, sizeof st);
        if (dfs(i)) res++;
    }
    printf("%d\n", n - res);
    return 0;
}