> #include<stdio.h>
> #include<stdlib.h>
> #include<memory.h>
> #define GSIZE 10010
> #define ESIZE 50010
> 
> int order[GSIZE],e,visit[GSIZE],flag[GSIZE],out[ESIZE],in[ESIZE],degree[GSIZE];
> struct Point
> {
> 	int id;
> 	struct Point *next;
> }mapa[GSIZE],mapt[GSIZE];
> void insert(int a, int b)
> {
> 	Point *p = &mapa[a];
> 	while(p->next )
> 		p = p->next;
> 	p->next = (struct Point *)malloc(sizeof(struct Point));
> 	p = p->next;
> 	p->id = b;
> 	p->next = NULL;
> 	p = &mapt[b];
> 	while(p->next )
> 		p = p->next;
> 	p->next = (struct Point *)malloc(sizeof(struct Point));
> 	p = p->next;
> 	p->id = a;
> 	p->next = NULL;
> }
> void dfsa(Point *k)
> {	
> 	visit[k->id] = true;
> 	Point *p = k->next;
> 	while(p){
> 		if(!visit[p->id]){
> 			p = &mapa[p->id];
> 			dfsa(p);
> 		}
> 		p = p->next;
> 	}
> 	order[e++] = k->id;
> }
> void dfst(Point *k)
> {
> 	visit[k->id] = true;
> 	Point *p = k->next;
> 	flag[k->id] = e;
> 	while(p != NULL){
> 		if(!visit[p->id]){
> 			p = &mapt[p->id];
> 			dfst(p);
> 		}
> 		p = p->next;
> 	}
> }
> int main()
> {
> 	int n,m,i,x,y;
> 	scanf("%d%d",&n,&m);
> 	for(i = 1; i <= n; i++){
> 		mapa[i].next = NULL;
> 		mapa[i].id = i;
> 		mapt[i].next = NULL;
> 		mapt[i].id = i;
> 	}
> 	for(i = 0; i < m; i++){
> 		scanf("%d %d",&x,&y);
> 		insert(x,y);
> 		out[i] = x;
> 		in[i] = y;
> 	}
> 	Point *temp;
> 	memset(visit,0,sizeof(visit));
> 	e = 0;
> 	for(i = 1; i <= n; i++){
> 		if(!visit[i]){
> 			temp = &mapa[i];
> 			dfsa(temp);
> 		}
> 	}
> 	e = 0;
> 	memset(flag,0,sizeof(flag));
> 	memset(visit,0,sizeof(visit));
> 	for(i = n-1; i >= 0; i--){
> 		if(!visit[order[i]]){
> 			temp = &mapt[order[i]];
> 			dfst(temp);
> 			e++;
> 		}
> 	}
> 	memset(degree,0,sizeof(degree));
> 	for(i = 0; i < m; i++){
> 		int eee = flag[out[i]];
> 		int sss = flag[in[i]];
> 		if(eee != sss)
> 			degree[eee]++;
> 	}
> 	int pos,tflag = 0;
> 	for(i = 0; i < e; i++){
> 		if(degree[i] == 0){
> 			pos = i;
> 			tflag++;
> 		}
> 	}
> 	if(tflag != 1)
> 		printf("0\n");
> 	else{
> 		int out = 0;
> 		for(i = 1; i <= n; i++)
> 			if(flag[i] == pos)
> 				out++;
> 			printf("%d\n",out);
> 	}
> 	return 0;
> }