1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 #include<stack>
 5 #include<vector>
 6 using namespace std;
 7 
 8 const int maxn=20005;
 9 vector<int>G[maxn];
10 stack<int>s;
11 int in[maxn],out[maxn],dfn[maxn],lowlink[maxn],sccno[maxn];
12 int scc_cnt,dfs_clock;
13 int m,n;
14 
15 void init()
16 {
17     for(int i=1;i<=n;i++)G[i].clear();
18     memset(in,0,sizeof(in));
19     memset(out,0,sizeof(out));
20     memset(dfn,0,sizeof(dfn));
21     memset(lowlink,0,sizeof(lowlink));
22     memset(sccno,0,sizeof(sccno));
23     scc_cnt=dfs_clock=0;
24 }
25 
26 void tarjan(int u)
27 {
28     lowlink[u]=dfn[u]=++dfs_clock;
29     s.push(u);
30     for(int i=0;i<G[u].size();i++)
31     {
32         int v=G[u][i];
33         if(!dfn[v])
34         {
35             tarjan(v);
36             lowlink[u]=min(lowlink[u],lowlink[v]);
37         }
38         else if(!sccno[v])
39             lowlink[u]=min(lowlink[u],dfn[v]);
40     }
41     if(lowlink[u]==dfn[u])
42     {
43         scc_cnt++;
44         while(1)
45         {
46             int x=s.top();
47             s.pop();
48             sccno[x]=scc_cnt;
49             if(x==u)break;
50         }
51     }
52 }
53 
54 
55 
56 int main()
57 {
58     while(scanf("%d%d",&n,&m)!=EOF)
59     {
60         init();
61         for(int i=0;i<m;i++)
62         {
63             int u,v;
64             scanf("%d%d",&u,&v);
65             G[u].push_back(v);
66         }
67         for(int i=1;i<=n;i++)
68             if(!dfn[i])
69                 tarjan(i);
70         for(int i=1;i<=n;i++)
71             for(int j=0;j<G[i].size();j++)
72                 if(sccno[G[i][j]]!=sccno[i])
73                 {
74                     in[sccno[G[i][j]]]++;
75                     out[sccno[i]]++;
76                 }
77         int cnt1=0,cnt2=0;
78         for(int i=1;i<=scc_cnt;i++)
79         {
80             if(!in[i])
81                 cnt1++;
82             if(!out[i])
83                 cnt2++;
84         }
85         if(scc_cnt==1)
86             puts("0");
87         else
88             printf("%d\n",max(cnt1,cnt2));
89     }
90     return 0;
91 }