#include <stack>

 #include <cstdio>

 #include <cstring>

 #include <iostream>

 const int MAXN = ;

 int n, m, cnt, idx, size, ans;

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

 int dfn[MAXN], low[MAXN], belong[MAXN], tot[MAXN];

 bool ins[MAXN];

 std::stack <int> s;

 inline int read()

 {

     int x = , f = ;

     char ch = getchar();

     for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -;

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

     return x * f;

 }

 inline int min(int x, int y)

 {

     return x < y ? x : y;

 }

 inline void add(int x, int y)

 {

     to[cnt] = y;

     next[cnt] = head[x];

     head[x] = cnt++;

 }

 inline void dfs(int u)

 {

     int i, v;

     s.push(u);

     ins[u] = ;

     dfn[u] = low[u] = ++idx;

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

     {

         v = to[i];

         if(!dfn[v])

         {

             dfs(v);

             low[u] = min(low[u], low[v]);

         }

         else if(ins[v]) low[u] = min(low[u], dfn[v]);

     }

     if(low[u] == dfn[u])

     {

         size++;

         do

         {

             v = s.top();

             s.pop();

             ins[v] = ;

             belong[v] = size;

         }

         while(u ^ v);

     }

 }

 int main()

 {

     int i, x, y;

     n = read();

     m = read();

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

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

     {

         x = read();

         y = read();

         add(x, y);

     }

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

         if(!dfn[i])

             dfs(i);

     for(i = ; i <= n; i++) tot[belong[i]]++;

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

         if(tot[i] > )

             ans++;

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

     return ;

 }