#include <iostream>

 #include <cstdio>

 #include <cmath>

 #include <vector>

 #include <cstring>

 #include <algorithm>

 #include <string>

 #include <set>

 #include <functional>

 #include <numeric>

 #include <sstream>

 #include <stack>

 #include <map>

 #include <queue>

 #define CL(arr, val)    memset(arr, val, sizeof(arr))

 #define ll long long

 #define inf 0x7f7f7f7f

 #define lc l,m,rt<<1

 #define rc m + 1,r,rt<<1|1

 #define pi acos(-1.0)

 #define L(x)    (x) << 1

 #define R(x)    (x) << 1 | 1

 #define MID(l, r)   (l + r) >> 1

 #define Min(x, y)   (x) < (y) ? (x) : (y)

 #define Max(x, y)   (x) < (y) ? (y) : (x)

 #define E(x)        (1 << (x))

 #define iabs(x)     (x) < 0 ? -(x) : (x)

 #define OUT(x)  printf("%I64d\n", x)

 #define lowbit(x)   (x)&(-x)

 #define Read()  freopen("a.txt", "r", stdin)

 #define Write() freopen("dout.txt", "w", stdout);

 using namespace std;

 #define N 20100

 //N为最大点数

 #define M 150100

 //M为最大边数

 int n, m;//n m 为点数和边数

 struct Edge{

     int from, to, nex;

     bool sign;//是否为桥

 }edge[M<<];

 int head[N], edgenum;

 void add(int u, int v){//边的起点和终点

     Edge E={u, v, head[u], false};

     edge[edgenum] = E;

     head[u] = edgenum++;

 }

 int DFN[N], Low[N], Stack[N], top, Time; //Low[u]是点集{u点及以u点为根的子树} 中(所有反向弧)能指向的(离根最近的祖先v) 的DFN[v]值(即v点时间戳)

 int taj;//连通分支标号，从1开始

 int Belong[N];//Belong[i] 表示i点属于的连通分支

 bool Instack[N];

 vector<int> bcc[N]; //标号从1开始

 void tarjan(int u ,int fa){

     DFN[u] = Low[u] = ++ Time ;

     Stack[top ++ ] = u ;

     Instack[u] =  ;

     for (int i = head[u] ; ~i ; i = edge[i].nex ){

         int v = edge[i].to ;

         if(DFN[v] == -)

         {

             tarjan(v , u) ;

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

             if(DFN[u] < Low[v])

             {

                 edge[i].sign = ;//为割桥

             }

         }

         else if(Instack[v]) Low[u] = min(Low[u] ,DFN[v]) ;

     }

     if(Low[u] == DFN[u]){

         int now;

         taj ++ ; bcc[taj].clear();

         do{

             now = Stack[-- top] ;

             Instack[now] =  ;

             Belong [now] = taj ;

             bcc[taj].push_back(now);

         }while(now != u) ;

     }

 }

 void tarjan_init(int all){

     memset(DFN, -, sizeof(DFN));

     memset(Instack, , sizeof(Instack));

     top = Time = taj = ;

     for(int i=;i<=all;i++)if(DFN[i]==- )tarjan(i, i); //注意开始点标！！！

 }

 vector<int>G[N];

 int du[N];

 void suodian(){

     memset(du, , sizeof(du));

     for(int i = ; i <= taj; i++)G[i].clear();

     for(int i = ; i < edgenum; i++){

         int u = Belong[edge[i].from], v = Belong[edge[i].to];

         if(u!=v)

         {

             G[u].push_back(v), du[v]++;

            // printf("%d %d\n",u,v);

         }

     }

 }

 void init(){memset(head, -, sizeof(head)); edgenum=;}

 int main()

 {

     //Read();

     int a,b;

     while(~scanf("%d%d",&n,&m))

     {

         init();

         //scanf("%d%d",&n,&m);

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

         {

             scanf("%d%d",&a,&b);

             add(a,b);

         }

         tarjan_init(n);

         suodian();

         if(taj==) {printf("0\n");continue;} //图本来就是强连通

         int x1=,x2=;

         for(int i=;i<=taj;i++)

         {

             if(G[i].size()==) x1++; //出度为0的点的个数

             if(du[i]==) x2++; //入度为0点的个数

         }

         //printf("%d %d\n",x1,x2);

         printf("%d\n",max(x1,x2));

     }

     return ;

 }