#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<vector>
#include<cstdio>
#include<queue>
using namespace std;

const int N=1000010;
const int M=1000010;
int n,m,ans;

struct Graph{
	int tot,head[M],suiv[N],ver[N],ind[N],vis[N];

	inline void lnk(int x,int y)
	{
		ver[++tot]=y;
		suiv[tot]=head[x];
		head[x]=tot;
		ind[y]++;
	}

	inline void topo()
	{
		queue<int>q;
		q.push(1);
		while(q.size())
		{
			int x=q.front();q.pop();
			for(int i=head[x];i;i=suiv[i])
			{
				int y=ver[i];
				if(vis[x]&&vis[y])ans++;
				else vis[x]=vis[y]=1;
				if(!--ind[y])q.push(y);
			}
		}
	}
}e;

int main()
{
	scanf("%d%d",&n,&m);
	for(int i=1,x,y;i<=m;i++)
		scanf("%d%d",&x,&y),e.lnk(x,y);
	e.topo();
	if(!e.vis[n])puts("0");
	else printf("%d\n",ans+1);
	return 0;
}