#include <cstdio>
#include <vector>
#include <cstring>
using namespace std;
const int NMAX = 8191;
int l[NMAX + 5] , r[NMAX + 5] , viz[NMAX + 5] , in[NMAX + 5];
vector <int> G[NMAX + 5] , T[NMAX + 5];
int path(int u)
{
    if(viz[u] == 1)
        return 0;
    viz[u] = 1;
    for(int j = 0 ; j < G[u].size() ; j ++)
    {
        int v = G[u][j];
        if(!r[v] || path(r[v]))
        {
            l[u] = v;
            r[v] = u;
            return 1;
        }
    }
    return 0;
}
int main()
{
    freopen("felinare.in" , "r" , stdin);
    freopen("felinare.out" , "w" , stdout);
    int n , m , e , x , y , i , j , cuplaj , gasit;
    scanf("%d%d" , &n , &m);
    for(i = 1 ; i <= m ; i ++)
    {
        scanf("%d%d" , &x , &y);
        T[x].push_back(y);
        in[y] ++;
    }
    cuplaj = 0;
    for(i = 1 ; i <= n ; i ++)
    {
        for(j = 0 ; j < T[i].size() ; j ++)
            viz[T[i][j]] = 1;
        for(j = 1 ; j <= n ; j ++)
            if(!viz[j] && i != j)
                G[i].push_back(j);
        memset(viz , 0, sizeof(viz));
        if(T[i].size() == 0 || in[i] == 0)
            cuplaj ++;
    }
    do
    {
        gasit = 0;
        memset(viz , 0 , sizeof(viz));
        for(i = 1 ; i <= n ; i ++)
            if(!l[i] && path(i))
            {
                gasit = 1;
                cuplaj ++;
            }
    }
    while(gasit);
    printf("%d\n" , cuplaj);
    return 0;
}