#include <cstdio>#include <algorithm>#include <vector>#include <cstring> using namespace std;const int MAX_V=10000;int V; //顶点数vector<int> G[MAX_V]; //图的邻接表表示vector<int> rG[MAX_V]; //反向图vector<int> vs; //后序遍历bool used[MAX_V];int cmp[MAX_V]; //所属强连通分量的拓扑序void add_edge(int from,int to){    G[from].push_back(to);    rG[to].push_back(from);} void dfs(int v){    used[v]=1;    for(int i=0;i<G[v].size();i++){        if(!used[G[v][i]])dfs(G[v][i]);    }vs.push_back(v);}void rdfs(int v,int k){    used[v]=1;    cmp[v]=k;    for(int i=0;i<rG[v].size();i++){        if(!used[rG[v][i]])rdfs(rG[v][i],k);    }}int scc(){    memset(used,0,sizeof(used));    vs.clear();    for(int v=0;v<V;v++){if(!used[v])dfs(v);}    memset(used,0,sizeof(used));    int k=0;    for(int i=vs.size()-1;i>=0;i--){        if(!used[vs[i]])rdfs(vs[i],k++);    }return k;}const int MAX_M=50000;int N,M;int A[MAX_M],B[MAX_M];int cnt[MAX_M];void solve(){    V=N;    for(int i=0;i<M;i++){        add_edge(A[i]-1,B[i]-1);    }int n=scc();    int num=0;    memset(cnt,0,sizeof(cnt));    for(int i=0;i<V;i++)++cnt[cmp[i]];    for(int i=0;i<n;i++)if(cnt[i]>1)num++;    printf("%d\n",num);}int main(){    while(~scanf("%d%d",&N,&M)){        for(int i=0;i<M;i++)scanf("%d%d",&A[i],&B[i]);        solve();    }return 0;}