#include <algorithm>
#include  <iterator>
#include  <iostream>
#include   <cstring>
#include   <cstdlib>
#include   <iomanip>
#include    <bitset>
#include    <cctype>
#include    <cstdio>
#include    <string>
#include    <vector>
#include     <stack>
#include     <cmath>
#include     <queue>
#include      <list>
#include       <map>
#include       <set>
#include   <cassert>

/*
        
⊂_ヽ
　 ＼＼ Λ＿Λ  来了老弟
　　 ＼(‘?‘)
　　　 >　⌒ヽ
　　　/ 　 へ＼
　　 /　　/　＼＼
　　 ?　ノ　　 ヽ_つ
　　/　/
　 /　/|
　(　(ヽ
　|　|、＼
　| 丿 ＼ ⌒)
　| |　　) /
‘ノ )　　L?

*/

using namespace std;
#define lson (l , mid , rt << 1)
#define rson (mid + 1 , r , rt << 1 | 1)
#define debug(x) cerr << #x << " = " << x << "\n";
#define pb push_back
#define pq priority_queue



typedef long long ll;
typedef unsigned long long ull;
//typedef __int128 bll;
typedef pair<ll ,ll > pll;
typedef pair<int ,int > pii;
typedef pair<int,pii> p3;

//priority_queue<int> q;//这是一个大根堆q
//priority_queue<int,vector<int>,greater<int> >q;//这是一个小根堆q
#define fi first
#define se second
//#define endl ‘\n‘

#define boost ios::sync_with_stdio(false);cin.tie(0)
#define rep(a, b, c) for(int a = (b); a <= (c); ++ a)
#define max3(a,b,c) max(max(a,b), c);
#define min3(a,b,c) min(min(a,b), c);


const ll oo = 1ll<<17;
const ll mos = 0x7FFFFFFF;  //2147483647
const ll nmos = 0x80000000;  //-2147483648
const int inf = 0x3f3f3f3f;
const ll inff = 0x3f3f3f3f3f3f3f3f; //18
const int mod = 1e9+7;
const double esp = 1e-8;
const double PI=acos(-1.0);
const double PHI=0.61803399;    //黄金分割点
const double tPHI=0.38196601;


template<typename T>
inline T read(T&x){
    x=0;int f=0;char ch=getchar();
    while (ch<‘0‘||ch>‘9‘) f|=(ch==‘-‘),ch=getchar();
    while (ch>=‘0‘&&ch<=‘9‘) x=x*10+ch-‘0‘,ch=getchar();
    return x=f?-x:x;
}

inline void cmax(int &x,int y){if(x<y)x=y;}
inline void cmax(ll &x,ll y){if(x<y)x=y;}
inline void cmin(int &x,int y){if(x>y)x=y;}
inline void cmin(ll &x,ll y){if(x>y)x=y;}

/*-----------------------showtime----------------------*/
            const int maxn = 1e5+9;
            vector<int>mp1[maxn],mp2[2][maxn];
            int dfn[maxn],low[maxn],vis[maxn],gtot,nn,dp[maxn];
            int col[maxn],vv[maxn];
            stack<int>st;   

            void tarjan(int u){
                dfn[u] = low[u] = ++gtot;
                st.push(u); vis[u] = 1;
                for(int i=0; i<mp1[u].size(); i++){
                    int v = mp1[u][i];
                    if(dfn[v] == 0) {
                        tarjan(v);
                        low[u] = min(low[u], low[v]);
                    }
                    else if(vis[v]){
                        low[u] = min(low[u], dfn[v]);
                    }
                }
                if(low[u] == dfn[u]){
                    int x;nn++;
                    while(!st.empty()){
                        int x = st.top(); st.pop();
                        col[x] = nn;
                        vis[x] = 0;
                        dp[nn]++;
                        if(x == u) break;
                    }
                }
            }
            int ans = 0;
            int dis[maxn][2];
            pii edge[maxn];
            void dji(int s,int id){
                priority_queue<pii>que;

                dis[s][id] = dp[s];
                que.push(pii(dis[s][id], s));
                while(!que.empty()){
                    int u = que.top().se; que.pop();

                    for(int i=0; i<mp2[id][u].size(); i++) {
                        int v = mp2[id][u][i],w = dp[v];

                        if(dis[v][id] < dis[u][id] + w){
                            dis[v][id] = dis[u][id] + w;
                            que.push(pii(dis[v][id], v));
                        }
                    }
                }
            }
int main(){
            int n,m;
            scanf("%d%d", &n, &m);
            rep(i, 1, m) {
                int x,y;    scanf("%d%d", &x, &y);
                mp1[x].pb(y);
                edge[i] = pii(x, y);
            } 
            for(int i=1; i<=n; i++)
                if(!dfn[i])tarjan(i);

            int s = col[1];
            int pp = 0;
            memset(vis, 0, sizeof(vis));
            for(int i=1; i<=n; i++){
                int u = col[i];
                if(u == 0) continue;

                for(int j=0; j<mp1[i].size(); j++){
                    int v = col[mp1[i][j]];
                    if(v == 0 || u == v) continue;
                    

                    mp2[0][u].pb(v);
                    mp2[1][v].pb(u);
                }
            }   
            dji(s, 0);

            dji(s, 1);

            int ans = dp[s];
            for(int i=1; i<=m; i++){
                int u = col[edge[i].fi],v = col[edge[i].se];
                if(dis[v][0] && dis[u][1])ans = max(ans, dis[v][0] + dis[u][1] - dp[s]);
            }

            printf("%d\n", ans);
            return 0;
}