> #include <iostream>
> #include <ctime>
> #include <cstdlib>
> #include <cstring>
> using namespace std;
> const int MAX=10010;
> 
> struct Fu
> {
>     int x;
>     int cut;
>     int kind;
> } fu[MAX];
> 
> int N,M;
> int graph[MAX][MAX];
> int flag[MAX];
> int counts=1;
> int kind=0;
> void DFS(int x);
> int compare(const void *a,const void *b);
> int compare1(const void *a,const void *b);
> int main()
> {
>     cin>>N>>M;
>     int i,j;
>     int x,y;
>     for(i=1;i<=N;i++)
>     	fu[i].x=i;
>     for(i=1; i<=M; i++)
>     {
>         cin>>x>>y;
>         graph[x][y]=1;
>     }
>     clock_t start_time=clock();///程序开始运行
> 
>     for(i=1; i<=N; i++)
>     {
> 		if(!flag[i])
>             DFS(i);
>     }
> 
>     for(i=2; i<=N; i++)
>         for(j=1; j<i; j++)
>         {
>             if(graph[i][j]+graph[j][i]==1)
>             {
>                 graph[i][j]=(graph[i][j]+1)%2;
>                 graph[j][i]=(graph[j][i]+1)%2;
>             }
> 
>         }
>     qsort(&fu[1],N,sizeof(struct Fu),compare);
>     memset(&flag[1],0,(N+1)*sizeof(int));
> 
>     for(i=1; i<=N; i++)
>         if(!flag[fu[i].x])
>         {
>             kind++;
>             DFS(fu[i].x);
>         }
>     int ans[MAX];
>     int flags;
>     memset(&ans[1],0,kind*sizeof(int));
> 	counts=0;
>     for(i=2; i<=N; i++)
>         for(j=1; j<i; j++)
>         {
>             if(graph[i][j]+graph[j][i]==1)
>             {
>                 graph[i][j]=(graph[i][j]+1)%2;
>                 graph[j][i]=(graph[j][i]+1)%2;
>             }
>         }
> 
>     for(i=1; i<=N; i++)
>     {
>         flags=0;
>         if(ans[fu[i].kind]!=-1)
>             for(j=i+1; j<=N; j++)
>             {
>                 if(graph[i][j]&&fu[i].kind!=fu[j].kind)
>                         ans[fu[i].kind]=-1;
> 
>                 if(graph[j][i]&&fu[i].kind!=fu[j].kind)
>                         ans[fu[j].kind]=-1;
>             }
>     }
>     int mark=0,result=0;
>     for(i=1;i<=kind;i++)
>         if(ans[i]!=-1)
>         {
>             mark++;
>             if(mark==1)
>                 result=i;
>         }
>     if(mark>1)  
>         cout<<0;
>     if(mark==1)
>     {
>     mark=0;
>     for(i=1;i<=N;i++)
>         if(fu[i].kind==result)
>         mark++;
>     cout<<mark;
>     }
>     
>     return 0;
> }
> 
> void DFS(int x)
> {
>     int i;
>     flag[x]=1;
>     fu[x].kind=kind;
>     for(i=1; i<=N; i++)
>     {
>         if(graph[x][i]&&!flag[i])
>             DFS(i);
>     }
>     fu[x].cut=counts++;
> }
> int compare(const void *a,const void *b)
> {
>     return ((struct Fu*)b)->cut-((struct Fu*)a)->cut;
> 
> }