stablegradients/pie-gem5-pairs huggingface dataset:
// Slower C++ solution:
#include <bits/stdc++.h>

using namespace std;

int n , m;

vector<vector<int>>vi(200005);

map<int,int>mp;

int mem[200005];

bool ok[200005];

int dfs(int node){

	if(mem[node])

		return mem[node];

	for(auto it : vi[node]){

		mem[node] = max(dfs(it) + 1 , mem[node]);

	}

	return mem[node];

}

int main() {

	memset(mem,0,sizeof(mem));

	cin>>n>>m;

	for(int i = 0 ; i < m ; i++){

		int x , y ; cin>>x>>y;

		vi[x].push_back(y);

		mp[y]++;

	}

	for(int i  = 1 ; i <= n ; i++){

		if(!mp[i]){

			dfs(i);

		}

	}

	int ans = 0;

	for(int i = 1 ; i <=  n; i++)

		ans = max(ans,mem[i]);

	cout<<ans;

	return 0;

}


// Faster C++ solution for the same problem (measured speedup: 5.297246658841329x):
#include <bits/stdc++.h>



using namespace std;



#define F first

#define S second

#define modulo ll (1e9 + 7)



typedef long long ll;

typedef pair<int,int> pii;



void init(){

    cin.tie(0);

    cin.sync_with_stdio(0);

}



const int N = 1e5 + 9, M = 1e6 + 9, OO = 0x3f3f3f3f;

const ll llOO = 0x3f3f3f3f3f3f3f3f;





#define neig(a, u, e, v) for(int v, e = (a).head[u] ; ~e and (v = (a).to[e], 1) ; e = (a).nxt[e])



struct Adj {

	int head[N], nxt[M], to[M], ne, n;

	void init(int n) {

		memset(head, -1, n * sizeof(head[0]));

		ne = 0;

		this->n = n;

	}

	void addEdge(int f, int t) {

		nxt[ne] = head[f];

		to[ne] = t;

		head[f] = ne++;

	}

	void addBiEdge(int f, int t) {

		addEdge(f, t);

		addEdge(t, f);

	}

	int addNode() {

		head[++n] = 0;

		return n;

	}

} adj;







int dp[N];



int dfs(int u){

    int &ret = dp[u];

    if(~ret)    return dp[u];



    ret = 0;

    neig(adj, u, e, v)

        ret = max(ret, dfs(v));



    ret++;



    return ret;

}





int n, m, u, v;



void go(int tc){

    cin >> n >> m;

    adj.init(n);

    for(int i = 0;i < m;i++){

        cin >> u >> v;  u--, v--;

        adj.addEdge(u, v);

    }



    memset(dp, -1, sizeof dp);



    int ans = 0;

    for(int i = 0;i < n;i++)

        ans = max(ans, dfs(i));



    cout << ans - 1;

}



int main(){

    init();



    int t, tc = 1;  t = 1;//cin >> t;

    while(t--)  go(tc++);



}
// Slower C++ solution:
/******

author :- Mahmoud Tarek.

*******/



#include<bits/stdc++.h>



using namespace std ;



#define rg register

#define dbg(v) cerr << #v << " " << v ;

typedef long long ll ;



const int N = 1e5 + 5 ;

vector<int> adj[N] ;

int n, m, a, b ;

int dp[N] ;



int solve(int i){



   if(i != 0 && !adj[i].size()){

     return 0 ;

   }



   int & ret = dp[i] ;

   if(~ret) return ret ;

   ret = 0 ;

   if(i == 0){

      for(int j = 1 ; j <= n ; j++)

        ret = max(ret, solve(j)) ;

   }



   for(auto j: adj[i]){

      ret = max(ret, 1 + solve(j)) ;

   }



   return ret ;

}



int main() {

//  freopen("in.txt", "r", stdin) ;



    cin >> n >> m ;

    for(int i = 0 ; i < m ; i++){

        cin >> a >> b ;

        adj[a].push_back(b) ;

    }



    memset(dp, -1, sizeof dp) ;

    cout << solve(0) ;



}





/*

  Empty set of troubles.

*/




// Faster C++ solution for the same problem (measured speedup: 2.7886066984189943x):
#include <bits/stdc++.h>



using namespace std;



#define F first

#define S second

#define modulo ll (1e9 + 7)



typedef long long ll;

typedef pair<int,int> pii;



void init(){

    cin.tie(0);

    cin.sync_with_stdio(0);

}



const int N = 1e5 + 9, M = 1e6 + 9, OO = 0x3f3f3f3f;

const ll llOO = 0x3f3f3f3f3f3f3f3f;





#define neig(a, u, e, v) for(int v, e = (a).head[u] ; ~e and (v = (a).to[e], 1) ; e = (a).nxt[e])



struct Adj {

	int head[N], nxt[M], to[M], ne, n;

	void init(int n) {

		memset(head, -1, n * sizeof(head[0]));

		ne = 0;

		this->n = n;

	}

	void addEdge(int f, int t) {

		nxt[ne] = head[f];

		to[ne] = t;

		head[f] = ne++;

	}

	void addBiEdge(int f, int t) {

		addEdge(f, t);

		addEdge(t, f);

	}

	int addNode() {

		head[++n] = 0;

		return n;

	}

} adj;







int dp[N];



int dfs(int u){

    int &ret = dp[u];

    if(~ret)    return dp[u];



    ret = 0;

    neig(adj, u, e, v)

        ret = max(ret, dfs(v));



    ret++;



    return ret;

}





int n, m, u, v;



void go(int tc){

    cin >> n >> m;

    adj.init(n);

    for(int i = 0;i < m;i++){

        cin >> u >> v;  u--, v--;

        adj.addEdge(u, v);

    }



    memset(dp, -1, sizeof dp);



    int ans = 0;

    for(int i = 0;i < n;i++)

        ans = max(ans, dfs(i));



    cout << ans - 1;

}



int main(){

    init();



    int t, tc = 1;  t = 1;//cin >> t;

    while(t--)  go(tc++);



}
// Slower C++ solution:


#include<bits/stdc++.h>

using namespace std;



const int N = 1e5 + 5;

typedef long long ll;

vector<int> adj[N];

bool visited[N]={};

int nodesNum;

int dp[N];

void dfs(int node){

    if(visited[node])

        return;

visited[node]=1;

for(int i=0;i<adj[node].size();i++){

        int child=adj[node][i];

    if(!visited[child])

    dfs(child);

    dp[node]=max(1+dp[child],dp[node]);

}

}







int main()

{

   int edges;

   cin >> nodesNum >> edges;

   while (edges--)

   {

       int x, y;

       cin >> x >> y;

       adj[x].push_back(y);

   }

   for(int i=1;i<=nodesNum;i++){

        if(!visited[i])

      dfs(i);

   }

   int ans=0;

   for(int i=1;i<=nodesNum;i++){

    ans=max(ans,dp[i]);

   }

 cout<<ans;

   return 0;

}


// Faster C++ solution for the same problem (measured speedup: 2.503344424240135x):
#include <bits/stdc++.h>



using namespace std;



#define F first

#define S second

#define modulo ll (1e9 + 7)



typedef long long ll;

typedef pair<int,int> pii;



void init(){

    cin.tie(0);

    cin.sync_with_stdio(0);

}



const int N = 1e5 + 9, M = 1e6 + 9, OO = 0x3f3f3f3f;

const ll llOO = 0x3f3f3f3f3f3f3f3f;





#define neig(a, u, e, v) for(int v, e = (a).head[u] ; ~e and (v = (a).to[e], 1) ; e = (a).nxt[e])



struct Adj {

	int head[N], nxt[M], to[M], ne, n;

	void init(int n) {

		memset(head, -1, n * sizeof(head[0]));

		ne = 0;

		this->n = n;

	}

	void addEdge(int f, int t) {

		nxt[ne] = head[f];

		to[ne] = t;

		head[f] = ne++;

	}

	void addBiEdge(int f, int t) {

		addEdge(f, t);

		addEdge(t, f);

	}

	int addNode() {

		head[++n] = 0;

		return n;

	}

} adj;







int dp[N];



int dfs(int u){

    int &ret = dp[u];

    if(~ret)    return dp[u];



    ret = 0;

    neig(adj, u, e, v)

        ret = max(ret, dfs(v));



    ret++;



    return ret;

}





int n, m, u, v;



void go(int tc){

    cin >> n >> m;

    adj.init(n);

    for(int i = 0;i < m;i++){

        cin >> u >> v;  u--, v--;

        adj.addEdge(u, v);

    }



    memset(dp, -1, sizeof dp);



    int ans = 0;

    for(int i = 0;i < n;i++)

        ans = max(ans, dfs(i));



    cout << ans - 1;

}



int main(){

    init();



    int t, tc = 1;  t = 1;//cin >> t;

    while(t--)  go(tc++);



}
// Slower C++ solution:
#include <iostream>

#include <set>

#include <stack>

#include <vector>

#include <map>

#include <string>

#include <string.h>

#include <cstring>

#include <queue>

#include <algorithm>

#include <math.h>



using namespace std;



typedef long long ll;





const int N = 1e5 + 5;

typedef long long ll;

vector<int> adj[N];

bool visited[N] = {};

int nodesNum;

int dp[N];

void dfs(int node) {

	if (visited[node])

		return;

	visited[node] = 1;

	for (int i = 0; i < adj[node].size(); i++) {

		int child = adj[node][i];

		if (!visited[child])

			dfs(child);

		dp[node] = max(1 + dp[child], dp[node]);

	}

}







int main()

{

	int edges;

	cin >> nodesNum >> edges;

	while (edges--)

	{

		int x, y;

		cin >> x >> y;

		adj[x].push_back(y);

	}

	for (int i = 1; i <= nodesNum; i++) {

		if (!visited[i])

			dfs(i);

	}

	int ans = 0;

	for (int i = 1; i <= nodesNum; i++) {

		ans = max(ans, dp[i]);

	}

	cout << ans;

	return 0;

}

// Faster C++ solution for the same problem (measured speedup: 2.503344424240135x):
#include <bits/stdc++.h>



using namespace std;



#define F first

#define S second

#define modulo ll (1e9 + 7)



typedef long long ll;

typedef pair<int,int> pii;



void init(){

    cin.tie(0);

    cin.sync_with_stdio(0);

}



const int N = 1e5 + 9, M = 1e6 + 9, OO = 0x3f3f3f3f;

const ll llOO = 0x3f3f3f3f3f3f3f3f;





#define neig(a, u, e, v) for(int v, e = (a).head[u] ; ~e and (v = (a).to[e], 1) ; e = (a).nxt[e])



struct Adj {

	int head[N], nxt[M], to[M], ne, n;

	void init(int n) {

		memset(head, -1, n * sizeof(head[0]));

		ne = 0;

		this->n = n;

	}

	void addEdge(int f, int t) {

		nxt[ne] = head[f];

		to[ne] = t;

		head[f] = ne++;

	}

	void addBiEdge(int f, int t) {

		addEdge(f, t);

		addEdge(t, f);

	}

	int addNode() {

		head[++n] = 0;

		return n;

	}

} adj;







int dp[N];



int dfs(int u){

    int &ret = dp[u];

    if(~ret)    return dp[u];



    ret = 0;

    neig(adj, u, e, v)

        ret = max(ret, dfs(v));



    ret++;



    return ret;

}





int n, m, u, v;



void go(int tc){

    cin >> n >> m;

    adj.init(n);

    for(int i = 0;i < m;i++){

        cin >> u >> v;  u--, v--;

        adj.addEdge(u, v);

    }



    memset(dp, -1, sizeof dp);



    int ans = 0;

    for(int i = 0;i < n;i++)

        ans = max(ans, dfs(i));



    cout << ans - 1;

}



int main(){

    init();



    int t, tc = 1;  t = 1;//cin >> t;

    while(t--)  go(tc++);



}
// Slower C++ solution:
#include <bits/stdc++.h>

using namespace std;

int n , m;

vector<vector<int>>vi(200005);

map<int,int>mp;

int mem[200005];

bool ok[200005];

int dfs(int node){

	if(mem[node])

		return mem[node];

	for(auto it : vi[node]){

		mem[node] = max(dfs(it) + 1 , mem[node]);

	}

	return mem[node];

}

int main() {

	memset(mem,0,sizeof(mem));

	cin>>n>>m;

	for(int i = 0 ; i < m ; i++){

		int x , y ; cin>>x>>y;

		vi[x].push_back(y);

		mp[y]++;

	}

	for(int i  = 1 ; i <= n ; i++){

		if(!mp[i]){

			dfs(i);

		}

	}

	int ans = 0;

	for(int i = 1 ; i <=  n; i++)

		ans = max(ans,mem[i]);

	cout<<ans;

	return 0;

}


// Faster C++ solution for the same problem (measured speedup: 1.6472064503066675x):
#include<iostream>

#include<algorithm>

#include<iomanip>

#include<cmath>

#include<vector>

#include<queue>

#include<stack>

#include<set>

#include <cstdio>

#include<map>

#include<string>

#include<assert.h>

#include<unordered_map>

#include <cstring>//memset();

#define Amr_Abdelazim ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);

#define pb push_back

#define pp pop_back

#define ll long long

#define ld long double

#define pll pair<ll,ll> 

#define vll vector<ll> 

#define vvll vector<vector<ll> >  

#define vpll vector<pair<ll,ll> > 

#define all(v) v.begin(),v.end()

#define rep(i,n)   for(int i=0;i<n;i++)

#define repp(s,i,n)   for(int i=s;i<n;i++)

#define print(v) for(auto i:v)cout<<i<<" ";cout<<"\n"; 

#define mkp make_pair

#define clr(ar,v) memset(ar,v,sizeof(ar));

#define TC ll t;cin>>t;while(t--)

#define in_vec ll n;cin>>n;vll v(n);rep(i,n)cin >> v[i];

#define EPS 1e-9

using namespace std;

const int mod = 1000000007;

const int N = 1000005;

class cmp{

public:

	bool operator() (pair<ll, pll> &A, pair<ll, pll> &B){

		return A > B;

	}

};

bool by_sec(pll &A, pll &B){

	return A.second < B.second;

}

bool is(pll a, pll b){

	return !((a.first > b.second&&a.second > b.second) || (a.first < b.first&&a.second < b.first));

}

ld dist(pll p1, pll p2){

	return (ld)sqrt((ld)(p1.first - p2.first)*(p1.first - p2.first) + (ld)(p1.second - p2.second)*(p1.second - p2.second));

}

vvll vv(100000+9);

ll dp[100000 + 9];

ll path(ll n){

	if (vv[n].size() == 0)return 0;

	if (dp[n] == -1){

		ll mx = -1;

		rep(i, vv[n].size())mx = max(mx, path(vv[n][i])+1);

		dp[n] = mx;

	}

	return dp[n];

}

int main()

{

	Amr_Abdelazim

		clr(dp, -1);

		ll n, m,ans=0;

	cin >> n >> m;

	while (m--){

		ll a, b;

		cin >> a >> b;

		vv[a].push_back(b);

	}

	repp(1, i, n + 1)

		ans = max(ans, path(i));

	cout << ans << "\n";

	return 0;

}
// Slower C++ solution:
#include <iostream>

#include <climits>

#include <cstring>

#include <vector>

using namespace std;

typedef long long int ll;

const ll inf = 1000000000000;

const ll maxn = 100010;

vector <ll> adj[maxn];

ll dp[maxn];



ll dfs(ll p){

    if(dp[p] != -1) return dp[p];

    ll maxpath = 0;

    for(auto x: adj[p]){

        maxpath = max(maxpath,1+dfs(x));

    }

    return dp[p] = maxpath;

}

int main(){

    memset(dp,-1,sizeof dp);



    ll n,k;



    scanf("%lld %lld",&n,&k);



    for(ll i = 0; i < k; i++){

        ll a,b;

        scanf("%lld %lld",&a,&b);

        adj[a].push_back(b);

    }

    ll ans = -1;

    for(ll i = 1; i <= n; i++){

        ans = max(ans,dfs(i));

    }

    printf("%lld\n",ans);

}


// Faster C++ solution for the same problem (measured speedup: 1.1009154224681377x):


#include <bits/stdc++.h>

#define inf INFINITY

#define file freopen( "input.txt" , "r" , stdin) ; freopen( "output.txt" , "w" , stdout) ;

#define Gamed ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);

#define _3102_ main()

#define endl '\n'

typedef long long ll;

typedef unsigned long long ull;

typedef long double ld;

using namespace std;

const int N = 1e5 + 100;

const ll MX = 1e18;

const ll mod = 1e9 + 7;

const double eps = 1e-9 ;

int n , m , dp[N] ;

vector < int > adj[N] ; 



int solve( int node ){

    //cout << node << endl ; 

    if ( dp[node] != -1 ) return dp[node] ;

    int maxi = 0 ; 

    for ( auto j : adj[node]){

        maxi = max ( maxi , solve(j) + 1 ) ;

    }

    return dp[node] = maxi ; 

} 



int _3102_{

	Gamed

    cin >> n >> m ; 

    for ( int i = 0 ; i < m ; i ++){

        int u , v ; 

        cin >> u >> v ;

        adj[v].push_back(u) ; 

    }

    //for ( int i = 1 ; i <= n ; i ++){

    //    cout << i << ": " ; 

    //    for ( auto j : adj[i] ){

    //        cout << j << " " ;

    //    }

    //    cout << endl ; 

    //}

    memset ( dp , -1 , sizeof dp ) ;

 

    for ( int i = 1 ; i <= n ; i ++){

        if ( dp[i] == -1 ){

            //cout << "--" << i << "--" << endl  ;

            solve (i) ;

            //cout << "------\n";

            //for ( int j = 1 ; j <= n ; j ++ ) cout << dp[j] << " " ;

            //cout << "\n------\n" ;  

        }  

    }

    int ans= 0 ; 

    for ( int i = 1 ; i <= n ; i ++ ){

        ans = max ( ans , dp[i]) ;

    }

    cout << ans << endl ; 

    return 0;

}
// Slower C++ solution:
#include <bits/stdc++.h>

using namespace std;

int n , m;

vector<vector<int>>vi(200005);

map<int,int>mp;

int mem[200005];

bool ok[200005];

int dfs(int node){

	if(mem[node])

		return mem[node];

	for(auto it : vi[node]){

		mem[node] = max(dfs(it) + 1 , mem[node]);

	}

	return mem[node];

}

int main() {

	memset(mem,0,sizeof(mem));

	cin>>n>>m;

	for(int i = 0 ; i < m ; i++){

		int x , y ; cin>>x>>y;

		vi[x].push_back(y);

		mp[y]++;

	}

	for(int i  = 1 ; i <= n ; i++){

		if(!mp[i]){

			dfs(i);

		}

	}

	int ans = 0;

	for(int i = 1 ; i <=  n; i++)

		ans = max(ans,mem[i]);

	cout<<ans;

	return 0;

}


// Faster C++ solution for the same problem (measured speedup: 1.8876800638613556x):


#include <bits/stdc++.h>

#define inf INFINITY

#define file freopen( "input.txt" , "r" , stdin) ; freopen( "output.txt" , "w" , stdout) ;

#define Gamed ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);

#define _3102_ main()

#define endl '\n'

typedef long long ll;

typedef unsigned long long ull;

typedef long double ld;

using namespace std;

const int N = 1e5 + 100;

const ll MX = 1e18;

const ll mod = 1e9 + 7;

const double eps = 1e-9 ;

int n , m , dp[N] ;

vector < int > adj[N] ; 



int solve( int node ){

    //cout << node << endl ; 

    if ( dp[node] != -1 ) return dp[node] ;

    int maxi = 0 ; 

    for ( auto j : adj[node]){

        maxi = max ( maxi , solve(j) + 1 ) ;

    }

    return dp[node] = maxi ; 

} 



int _3102_{

	Gamed

    cin >> n >> m ; 

    for ( int i = 0 ; i < m ; i ++){

        int u , v ; 

        cin >> u >> v ;

        adj[v].push_back(u) ; 

    }

    //for ( int i = 1 ; i <= n ; i ++){

    //    cout << i << ": " ; 

    //    for ( auto j : adj[i] ){

    //        cout << j << " " ;

    //    }

    //    cout << endl ; 

    //}

    memset ( dp , -1 , sizeof dp ) ;

 

    for ( int i = 1 ; i <= n ; i ++){

        if ( dp[i] == -1 ){

            //cout << "--" << i << "--" << endl  ;

            solve (i) ;

            //cout << "------\n";

            //for ( int j = 1 ; j <= n ; j ++ ) cout << dp[j] << " " ;

            //cout << "\n------\n" ;  

        }  

    }

    int ans= 0 ; 

    for ( int i = 1 ; i <= n ; i ++ ){

        ans = max ( ans , dp[i]) ;

    }

    cout << ans << endl ; 

    return 0;

}
// Slower C++ solution:
/*

	Author: Luis Manuel D�az Bar�n (LUISMO)

	Problem:

	Online Judge:

	Idea:

*/

#include<bits/stdc++.h>

// Types

#define ll long long

#define ull unsigned long long

// IO

#define sf scanf

#define pf printf

#define mkp make_pair

#define fi first

#define se second

#define endl "\n"



using namespace std;



typedef pair<int, int> pii;

typedef pair<ll, ll> pll;

const ll inf = 1e16 + 3;

const int mod = 1e9 + 7;

const int lim = 2e5 + 2;



int N, M;

vector<int> adj[lim];



int dp[lim];

bool mark[lim];



int DFS(int idx)

{

    if(mark[idx])

        return dp[idx];

    // for each adjacent

    for(int i = 0; i < adj[idx].size(); i++)

    {

        int nxt = adj[idx][i];

        int aux = DFS(nxt);

        dp[idx] = max(dp[idx], 1 + aux);

    }

    mark[idx] = true;

    return dp[idx];

}



void solve()

{

    cin >> N >> M;

    // reading edges

    for (int i = 0; i < M; i++)

    {

        int xi, yi;

        cin >> xi >> yi;

        adj[xi].push_back(yi);

    }

    

    int answ = 0;



    for(int i = 1; i <= N; i++)

    {

        int aux = DFS(i);

        answ = max(answ, aux);

    }



    cout << answ;

}



void fastIO()

{

	cin.sync_with_stdio(false);

	cin.tie(0);

}



void IO()

{

	if(fopen("d:\\lmo.in","r") != NULL)

	{

		freopen("d:\\lmo.in","r",stdin);

	}

	else if(fopen("/media/Beijing/lmo.in","r") != NULL)

	{

		freopen("/media/Beijing/lmo.in", "r", stdin);

	}

}



int main()

{

	IO();



	fastIO();



	solve();

}


// Faster C++ solution for the same problem (measured speedup: 1.6410750214085326x):
#include <bits/stdc++.h>

using namespace std;

#define ll long long

#define ull unsigned long long

#define PII pair<int,int>

#define PSI pair<string,int>

#define PIII pair< int, pair<int,int> >

const int MaxN = 1e5+5;

vector<int> g[MaxN];

int dp[MaxN];

int N;



int dfs(int node){



    auto &ret = dp[node];

    if(ret!=-1) return ret;

    

    ret = 0;

    for(auto i: g[node])

        ret = max(ret, dfs(i)+1 );



    return ret;

}



void read(){



    int edge;

    memset(dp, -1, sizeof dp);

    cin>>N>>edge;



    for(int i=0; i<edge; i++){

        int u,v;

        cin>>u>>v;

        g[u].push_back(v);

    }

}



void solve(){



    read();

    int res = 0;

    for(int i=1; i<=N; i++)

        res = max(res, dfs(i) );



    cout<< res << "\n";

}





int main(){



    //freopen("input.txt","r",stdin);

    ios_base::sync_with_stdio(false);

    cin.tie(nullptr);

    solve();



    return 0;

}
// Slower C++ solution:
#include <iostream>

#include <climits>

#include <cstring>

#include <vector>

using namespace std;

typedef long long int ll;

const ll inf = 1000000000000;

const ll maxn = 100010;

vector <ll> adj[maxn];

ll dp[maxn];



ll dfs(ll p){

    if(dp[p] != -1) return dp[p];

    ll maxpath = 0;

    for(auto x: adj[p]){

        maxpath = max(maxpath,1+dfs(x));

    }

    return dp[p] = maxpath;

}

int main(){

    memset(dp,-1,sizeof dp);



    ll n,k;



    scanf("%lld %lld",&n,&k);



    for(ll i = 0; i < k; i++){

        ll a,b;

        scanf("%lld %lld",&a,&b);

        adj[a].push_back(b);

    }

    ll ans = -1;

    for(ll i = 1; i <= n; i++){

        ans = max(ans,dfs(i));

    }

    printf("%lld\n",ans);

}


// Faster C++ solution for the same problem (measured speedup: 1.1001572867407856x):
#include <bits/stdc++.h>

using namespace std;

#define ll long long

#define ull unsigned long long

#define PII pair<int,int>

#define PSI pair<string,int>

#define PIII pair< int, pair<int,int> >

const int MaxN = 1e5+5;

vector<int> g[MaxN];

int dp[MaxN];

int N;



int dfs(int node){



    auto &ret = dp[node];

    if(ret!=-1) return ret;

    

    ret = 0;

    for(auto i: g[node])

        ret = max(ret, dfs(i)+1 );



    return ret;

}



void read(){



    int edge;

    memset(dp, -1, sizeof dp);

    cin>>N>>edge;



    for(int i=0; i<edge; i++){

        int u,v;

        cin>>u>>v;

        g[u].push_back(v);

    }

}



void solve(){



    read();

    int res = 0;

    for(int i=1; i<=N; i++)

        res = max(res, dfs(i) );



    cout<< res << "\n";

}





int main(){



    //freopen("input.txt","r",stdin);

    ios_base::sync_with_stdio(false);

    cin.tie(nullptr);

    solve();



    return 0;

}
// Slower C++ solution:
#include <bits/stdc++.h>

using namespace std;

int n , m;

vector<vector<int>>vi(200005);

map<int,int>mp;

int mem[200005];

bool ok[200005];

int dfs(int node){

	if(mem[node])

		return mem[node];

	for(auto it : vi[node]){

		mem[node] = max(dfs(it) + 1 , mem[node]);

	}

	return mem[node];

}

int main() {

	memset(mem,0,sizeof(mem));

	cin>>n>>m;

	for(int i = 0 ; i < m ; i++){

		int x , y ; cin>>x>>y;

		vi[x].push_back(y);

		mp[y]++;

	}

	for(int i  = 1 ; i <= n ; i++){

		if(!mp[i]){

			dfs(i);

		}

	}

	int ans = 0;

	for(int i = 1 ; i <=  n; i++)

		ans = max(ans,mem[i]);

	cout<<ans;

	return 0;

}


// Faster C++ solution for the same problem (measured speedup: 1.886380129580287x):
#include <bits/stdc++.h>

using namespace std;

#define ll long long

#define ull unsigned long long

#define PII pair<int,int>

#define PSI pair<string,int>

#define PIII pair< int, pair<int,int> >

const int MaxN = 1e5+5;

vector<int> g[MaxN];

int dp[MaxN];

int N;



int dfs(int node){



    auto &ret = dp[node];

    if(ret!=-1) return ret;

    

    ret = 0;

    for(auto i: g[node])

        ret = max(ret, dfs(i)+1 );



    return ret;

}



void read(){



    int edge;

    memset(dp, -1, sizeof dp);

    cin>>N>>edge;



    for(int i=0; i<edge; i++){

        int u,v;

        cin>>u>>v;

        g[u].push_back(v);

    }

}



void solve(){



    read();

    int res = 0;

    for(int i=1; i<=N; i++)

        res = max(res, dfs(i) );



    cout<< res << "\n";

}





int main(){



    //freopen("input.txt","r",stdin);

    ios_base::sync_with_stdio(false);

    cin.tie(nullptr);

    solve();



    return 0;

}