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

using namespace std;

const int N = 210, M = 30020;

bool d[N][N];
bool st[N];
int n, m;
int match[N];

bool find(int x){
    for(int i = 1;i <= n;i ++ )
        if(!st[i] && d[x][i]){
            st[i] = true;
            int t = match[i];
            if(!t || find(t)){
                match[i] = x;
                return true;
            }
        }
    return false;
}
int main(){

    cin >> n >> m;

    while(m -- ){
        int a, b;
        cin >> a >> b;
        d[a][b] = true;
    }
    //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 ++ )
                d[i][j] |= d[i][k] & d[k][j];

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

    cout << n - res << endl;
    return 0;
}