#include<cstdio>
#include<algorithm>
#define ll long long
using namespace std;
ll Read()
{
	ll Output=0;
	char Input=getchar();
	while(Input<'0'||Input>'9')
	Input=getchar();
	while(Input>='0'&&Input<='9')
	{
		Output=Output*10+Input-'0';
		Input=getchar();
	}
	return Output;
}
int N,M;
struct edge
{
	int Next,To;
	bool This;
}Edge[1000001];
int Head[1000001],Lon;
bool Vis[1000001];
bool Visable[1000001];
int Fa[1000001];
int Ans=1;
void Make(int From,int To)
{
	Edge[++Lon].Next=Head[From];
	Edge[Lon].To=To;
	Head[From]=Lon;
}
void DFS(int Pos)
{
	Vis[Pos]=true;
	Visable[Pos]=(Pos==N);
	for(int i=Head[Pos];i;i=Edge[i].Next)
	{
		int To=Edge[i].To;
		if(Vis[To])continue;
		Edge[i].This=true;
		Fa[To]=Pos;
		DFS(To);
		Visable[Pos]|=Visable[To];
	}
}
void Cover(int Pos)
{
	if(Visable[Pos])return;
	Visable[Pos]=true;
	Cover(Fa[Pos]);
}
int main()
{
	N=Read(),M=Read();
	for(int i=1;i<=M;++i)
	{
		int X=Read(),Y=Read();
		Make(X,Y);
	}
	DFS(1);
	if(!Vis[N])
	{
		puts("0");
		return 0;
	}
	for(int i=N;i>0;--i)
	{
		if(!Vis[i])continue;
		for(int j=Head[i];j;j=Edge[j].Next)
		{
			if(Edge[j].This)continue;
			if(Visable[Edge[j].To])
			Cover(i);
			Ans+=Visable[Edge[j].To];
		}
	}
	printf("%d\n",Ans);
}