1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <queue>
 5 #define INF 0x3fffffff
 6 #define inc(i,j,k) for(int i=j;i<=k;i++)
 7 using namespace std;
 8
 9 int n,m,a[200][200],s,t;
10 struct e{int t,c,n;}; e es[100000]; int ess,g[1000];
11 inline void pe(int f,int t,int c){
12     es[++ess]=(e){t,c,g[f]};g[f]=ess;es[++ess]=(e){f,0,g[t]};g[t]=ess;
13 }
14 void init(){ess=-1; memset(g,-1,sizeof(g));}
15 queue <int> q; int h[1000];
16 bool bfs(int s,int t){
17     while(! q.empty())q.pop(); memset(h,-1,sizeof(h)); h[s]=0; q.push(s);
18     while(! q.empty()){
19         int x=q.front(); q.pop();
20         for(int i=g[x];i!=-1;i=es[i].n)if(es[i].c&&h[es[i].t]==-1)h[es[i].t]=h[x]+1,q.push(es[i].t);
21     }
22     if(h[t]==-1)return 0;else return 1;
23 }
24 int dfs(int x,int t,int f){
25     if(x==t)return f; int used=0;
26     for(int i=g[x];i!=-1;i=es[i].n)if(es[i].c&&h[es[i].t]==h[x]+1){
27         int w=dfs(es[i].t,t,min(f,es[i].c));
28         es[i].c-=w; es[i^1].c+=w; used+=w; f-=w; if(f==0)return used;
29     }
30     if(used==0)h[x]=-1; return used;
31 }
32 int dinic(int s,int t){int ans=0; while(bfs(s,t))ans+=dfs(s,t,INF); return ans;};
33 int main(){
34     scanf("%d%d",&n,&m); memset(a,0,sizeof(a));
35     inc(i,1,m){int a1,b1; scanf("%d%d",&a1,&b1); a[a1][b1]=1;}
36     inc(k,1,n)inc(i,1,n)inc(j,1,n)a[i][j]|=a[i][k]&a[k][j];
37     s=0; t=n+n+1; init();
38     inc(i,1,n)pe(s,i,1),pe(i+n,t,1);
39     inc(i,1,n)inc(j,1,n)if(a[i][j])pe(i,j+n,1);
40     printf("%d",n-dinic(s,t));
41 }