#include <cstdio>

 #include <cstring>

 #include <iostream>

 const int MAXN = ;

 int n, m, ans, cnt;

 int a[MAXN][MAXN], belong[MAXN], head[MAXN], to[MAXN << ], next[MAXN << ];

 bool vis[MAXN];

 inline int read()

 {

     int x = ;

     char c = getchar();

     for(; !isdigit(c); c = getchar());

     for(; isdigit(c); c = getchar()) x = (x << ) + (x << ) + c - '';

     return x;

 }

 inline bool find(int u)

 {

     int i, v;

     for(i = head[u]; i ^ -; i = next[i])

     {

         v = to[i];

         if(!vis[v])

         {

             vis[v] = ;

             if(!belong[v] || find(belong[v]))

             {

                 belong[v] = u;

                 return ;

             }

         }

     }

     return ;

 }

 inline void add(int x, int y)

 {

     to[cnt] = y;

     next[cnt] = head[x];

     head[x] = cnt++;

 }

 int main()

 {

     int i, j, k, x, y;

     n = read();

     m = read();

     for(; m--;)

     {

         x = read();

         y = read();

         a[x][y] = ;

     }

     for(k = ; k <= n; k++)

         for(i = ; i <= n; i++)

             for(j = ; j <= n; j++)

                 a[i][j] |= (a[i][k] && a[k][j]);

     memset(head, -, sizeof(head));

     for(i = ; i <= n; i++)

         for(j = ; j <= n; j++)

             if(a[i][j])

                 add(i, j);

     ans = n;

     for(i = ; i <= n; i++)

     {

         memset(vis, , sizeof(vis));

         ans -= find(i);

     }

     printf("%d\n", ans);

     return ;

 }