#include <cstdio>

 #include <cstring>

 #define M(x, a) memset(a, x, sizeof(a))

 using namespace std;

 const int MAXN = ;

 int n, k, cnt, ans;

 int head[MAXN], next[MAXN * MAXN], to[MAXN * MAXN], belong[MAXN];

 bool vis[MAXN];

 inline void add(int x, int y)

 {

     to[cnt] = y;

     next[cnt] = head[x];

     head[x] = cnt++;

 }

 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 ;

 }

 int main()

 {

     int i, x, y;

     scanf("%d %d", &n, &k);

     M(-, head);

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

     {

         scanf("%d %d", &x, &y);

         add(x, y);

     }

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

     {

         M(, vis);

         if(find(i)) ans++;

     }

     printf("%d", ans);

     return ;

 }