#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define N 1000010
map<ll,ll>mp1,mp2;
vector<ll>g[N];
vector<ll>f[N];
void bfs1(ll x)
{
    queue<ll>q;
    q.push(x);
    while(!q.empty())
    {
        ll num=q.front();
        q.pop();
        for(auto b:g[num])
        {
            if(mp1[b])continue;
            else 
            {
                mp1[b]++;
                q.push(b);
            }
        }
    }
}
void bfs2(ll x)
{
    queue<ll>q;
    q.push(x);
    while(!q.empty())
    {
        ll num=q.front();
        q.pop();
        for(auto b:f[num])
        {
            if(mp2[b])continue;
            else 
            {
                mp2[b]++;
                q.push(b);
            }
        }
    }
}

struct node
{
    ll l,r;
}p[N];

void solve() {
    ll n,m;
    cin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        ll u,v;
        cin>>u>>v;
        g[u].push_back(v);
        f[v].push_back(u);
        p[i].l=u;p[i].r=v;
    }
    bfs1(1);
    bfs2(n);
    mp1[1]=1;mp2[1]=1;
    mp1[n]=1;mp2[n]=1;
    ll ans=0;
    for(int i=1;i<=m;i++)
    {
        if(mp1[p[i].l]&&mp1[p[i].r]&&mp2[p[i].l]&&mp2[p[i].r])
        {
            //cerr<<p[i].l<<" "<<p[i].r<<"\n";
            ans++;
        }
    }
    //cerr<<ans<<"\n";
    for(int i=2;i<n;i++)
    {
        if(mp1[i]&&mp2[i])ans--;
    }
    cout<<ans;
}

int main() {
    ios::sync_with_stdio(false);
    cout.tie(0);
    cin.tie(0);

    int T = 1;
    //cin >> T;
    for (int i = 1; i <= T; i++) {
        solve();
    }

    return 0;
}