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

using namespace std;

typedef long long int ll;



vector<ll>adj[100005];

bool visited[100005];

ll dp[100005];



void dfs(ll s)

{

    ll len=1;

    visited[s]=true;

    for(auto x : adj[s])

    {

        if(visited[x]==false)

            dfs(x);



        dp[s]=max(dp[s],len+dp[x]);

    }

}





int main()

{

    ll n,m,x,y;

    cin>>n>>m;

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

    {

        cin>>x>>y;

        adj[x].push_back(y);

        //adj[y].push_back(x);

    }



    ll mx_len=0;



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

    {

        if(visited[i]==false)

            dfs(i);

        

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

    }



    cout<<mx_len<<endl;



    return 0;

}




// Faster C++ solution for the same problem (measured speedup: 1.9371541355814013x):
#include<bits/stdc++.h>

#define int long long

#define fast ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0)

using namespace std;

#define endl '\n'

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

#define forj(s,n) for(int j=s;j<n;j++) 

#define vii vector<int>

int t = 1, n, m;

vector<vii> edges;

int dp[100000 + 1];

int solve(int i) {///1  2  

	if (edges[i].size() == 0) return 0;

	int& ret = dp[i];

	if (~ret) return ret;

	int r1 = 0;

	for (auto child : edges[i]) {

		r1 = max(r1, 1 + solve(child));

	}

	return ret=r1;

}

signed main()

{

	fast;

   //cin>>t;

	int u, v;

	while (t--)

	{

		memset(dp, -1, sizeof dp);

		cin >> n >> m;

		edges = vector<vii>(n + 1);

		while (m--) {

			cin >> u >> v;

			edges[u].push_back(v);

		}

		int ans = 0;

		fori(1, n + 1) {

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

		}

		cout << ans << endl;

	}

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

using namespace std;



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

#define fp(i,a,b) for(int i=a ; i<b ; i++)

#define fn(i,a,b) for(int i=a ; i>=b ; i--)

#define pb push_back

#define mk make_pair

#define ff first

#define ss second

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



typedef long long ll;

typedef pair<int,int> ii;

typedef vector<ii> vii;

typedef vector<int> vi;

typedef vector<ll> vll;



const int M=1e5+5;

const ll INF=1e15;

const int MOD=1e9+5;



int n,m,r;

int dp[M];

vi vec[M];



int DP(int x){

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

	dp[x] = 0;

	fp(i,0,vec[x].size()) dp[x] = max(dp[x] , DP(vec[x][i]) + 1);

	return dp[x];

}



int main(){



	fastio;

	cin >> n >> m;

	fp(i,1,n+1) dp[i] = -1;



	while (m--){

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

		vec[x].pb(y);

	}



	fp(i,1,n+1)

		if (dp[i] == -1) r = max(r,DP(i));



	cout << r << "\n";



	return 0;

}


// Faster C++ solution for the same problem (measured speedup: 1.9508869653650838x):
#include<bits/stdc++.h>

#define int long long

#define fast ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0)

using namespace std;

#define endl '\n'

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

#define forj(s,n) for(int j=s;j<n;j++) 

#define vii vector<int>

int t = 1, n, m;

vector<vii> edges;

int dp[100000 + 1];

int solve(int i) {///1  2  

	if (edges[i].size() == 0) return 0;

	int& ret = dp[i];

	if (~ret) return ret;

	int r1 = 0;

	for (auto child : edges[i]) {

		r1 = max(r1, 1 + solve(child));

	}

	return ret=r1;

}

signed main()

{

	fast;

   //cin>>t;

	int u, v;

	while (t--)

	{

		memset(dp, -1, sizeof dp);

		cin >> n >> m;

		edges = vector<vii>(n + 1);

		while (m--) {

			cin >> u >> v;

			edges[u].push_back(v);

		}

		int ans = 0;

		fori(1, n + 1) {

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

		}

		cout << ans << endl;

	}

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

using namespace std;

#define print printf("==================\n")

#define ll long long

#define pi acos(-1.0)

#define eps 1e-16

#define max3(a,b,c) max(a,max(b,c))

const ll INF = 1 << 30;

typedef pair<double, double  > payar;

typedef struct

{

    ll  x, y;

} point;

priority_queue<payar, vector<payar>,  greater<payar> > pq; ///accending

vector< pair<double,payar  > > vpp;

vector < payar >  vp;

vector<int>g[100005];

int ind[100005];

int vis[100005];

int dis[100005];



int dfs(int u)

{



    vis[u]=1;

    if(dis[u]!=-1)return dis[u];

    int maxi =0;

    for(auto it: g[u])

    {

       // static int k;

     //   cout<<k++<<" "<<it<<endl;



      dis[u]=  maxi=max(maxi,1+dfs(it) );

    }

    return maxi;

}

int main()

{



    int n, m ;

    cin>>n>>m;

    memset(dis,-1,sizeof dis);

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

    {

        int u, v;

        cin>>u>>v;

        g[u].push_back(v);

        ind[v]++;



    }

    int ans =0;

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

    {

        if(ind[i]==0 and vis[i]==0)

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

    }

    cout<<ans;

    return  0 ;

}


// Faster C++ solution for the same problem (measured speedup: 1.11675829560006x):
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;



int dp[100001];

bool visited[100001];

vector<int> graph[100001];

int ans;

void dfs(int node){

    visited[node] = true;

    if(graph[node].empty()){ dp[node] = 0; return;}

    int maxa =0;

    for(auto i : graph[node]){

        if(!visited[i]){

            dfs(i);

        }

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

    }

    dp[node] = 1 + maxa;

}

int n, m;

int main(){

    cin>>n>>m;

    while(m--){

        int u, v;

        cin>>u>>v;

        graph[u].push_back(v);

    }

    int ans = 0;

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

        dfs(x);

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

    }

    cout<<ans;



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

#define ll long long

using namespace std;

ll n,m,x,y;

vector<ll>v[100009];

ll dp[100009];



ll f(ll N){

	if (v[N].empty())return 0;

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

	ll z=0;

	for(int i=0; i<v[N].size(); i++){

		z=max(z,f(v[N][i])+1);

	}

	dp[N]=z;

	return dp[N];

}



int main(){

	cin >> n >> m;

	memset(dp,-1,sizeof dp);

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

		cin >> x >> y;

		v[x].push_back(y);

	}

	ll jwb=0;

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

		jwb=max(jwb,f(i));

	}

	cout << jwb << endl;

}

// Faster C++ solution for the same problem (measured speedup: 1.242064134857851x):
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;



int dp[100001];

bool visited[100001];

vector<int> graph[100001];

int ans;

void dfs(int node){

    visited[node] = true;

    if(graph[node].empty()){ dp[node] = 0; return;}

    int maxa =0;

    for(auto i : graph[node]){

        if(!visited[i]){

            dfs(i);

        }

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

    }

    dp[node] = 1 + maxa;

}

int n, m;

int main(){

    cin>>n>>m;

    while(m--){

        int u, v;

        cin>>u>>v;

        graph[u].push_back(v);

    }

    int ans = 0;

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

        dfs(x);

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

    }

    cout<<ans;



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

#define ll long long

using namespace std;

ll n,m,x,y;

vector<ll>v[100009];

ll dp[100009];



ll f(ll N){

	if (v[N].empty())return 0;

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

	ll z=0;

	for(int i=0; i<v[N].size(); i++){

		z=max(z,f(v[N][i])+1);

	}

	dp[N]=z;

	return dp[N];

}



int main(){

	cin >> n >> m;

	memset(dp,-1,sizeof dp);

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

		cin >> x >> y;

		v[x].push_back(y);

	}

	ll jwb=0;

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

		jwb=max(jwb,f(i));

	}

	cout << jwb << endl;

}//z

// Faster C++ solution for the same problem (measured speedup: 1.242064134857851x):
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;



int dp[100001];

bool visited[100001];

vector<int> graph[100001];

int ans;

void dfs(int node){

    visited[node] = true;

    if(graph[node].empty()){ dp[node] = 0; return;}

    int maxa =0;

    for(auto i : graph[node]){

        if(!visited[i]){

            dfs(i);

        }

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

    }

    dp[node] = 1 + maxa;

}

int n, m;

int main(){

    cin>>n>>m;

    while(m--){

        int u, v;

        cin>>u>>v;

        graph[u].push_back(v);

    }

    int ans = 0;

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

        dfs(x);

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

    }

    cout<<ans;



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





using namespace std;



vector<int> v[100005];

bool processado[100005];

int tab[100005];



int dfs(int s)

{



    //processado[s] = true;

    int soma, max = 0, entrou = 0;

    

    if(tab[s] >= 0)

    {

        return tab[s];

    }

    for (int i = 0; i < v[s].size(); ++i)

    {



        entrou = 1;

        soma = dfs(v[s][i]) + 1;

        if(soma > max)

        {

            max = soma;

            tab[s] = max;

        }

    }

    if(entrou == 1)

    {

        return max;

    }



    return tab[s] = 0;



}

 





int main(){



    int n, m;

    cin >> n >> m;

    memset(tab, -1, sizeof(tab));



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

    {

        processado[i] = false;

    }*/



    int x, y;

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

    {

        cin >> x >> y;

        v[x].push_back(y);

    }



    int soma = 0;

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

    {

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

    }



    cout << soma << endl;











    



    

    return 0;

}


// Faster C++ solution for the same problem (measured speedup: 1.1150350895840924x):
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;



int dp[100001];

bool visited[100001];

vector<int> graph[100001];

int ans;

void dfs(int node){

    visited[node] = true;

    if(graph[node].empty()){ dp[node] = 0; return;}

    int maxa =0;

    for(auto i : graph[node]){

        if(!visited[i]){

            dfs(i);

        }

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

    }

    dp[node] = 1 + maxa;

}

int n, m;

int main(){

    cin>>n>>m;

    while(m--){

        int u, v;

        cin>>u>>v;

        graph[u].push_back(v);

    }

    int ans = 0;

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

        dfs(x);

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

    }

    cout<<ans;



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

     **author : _KMS_

     **created : 30-03-2020

**/

#include<bits/stdc++.h>

using namespace std;

const long long M =3e5+10,MOD=1e9+7;

typedef long long ll;

vector<int>v[M];

bool vis[M];

int dp[M];

void dfs(int i)

{

  vis[i]=1;

  for(int j=0;j<v[i].size();j++)

  {

    int y=v[i][j];

    if(!vis[y])dfs(y);

    dp[i]=max(dp[i],dp[y]+1);

  }

}

int main()

{

    ios::sync_with_stdio(false);

    cin.tie(0);

     int n,m;

     cin>>n>>m;

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

     {

       int x,y;

       cin>>x>>y;

       v[x].push_back(y);

     }

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

     {

      if(!vis[i])

      {

        dfs(i);

      }

     }

    sort(dp+1,dp+n+1);

    cout<<dp[n]<<"\n";

    return 0;

}

// Faster C++ solution for the same problem (measured speedup: 2.6789594815875613x):
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;



int dp[100001];

bool visited[100001];

vector<int> graph[100001];

int ans;

void dfs(int node){

    visited[node] = true;

    if(graph[node].empty()){ dp[node] = 0; return;}

    int maxa =0;

    for(auto i : graph[node]){

        if(!visited[i]){

            dfs(i);

        }

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

    }

    dp[node] = 1 + maxa;

}

int n, m;

int main(){

    cin>>n>>m;

    while(m--){

        int u, v;

        cin>>u>>v;

        graph[u].push_back(v);

    }

    int ans = 0;

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

        dfs(x);

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

    }

    cout<<ans;



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

#define ll long long



using namespace std;

int dp[200005],n,m;

vector <int> DAG[200005];

int dfs(int x)

{

    if(dp[x]!=-1)

        return dp[x];

    int retVal=0;

    for(int i=0;i<DAG[x].size();i++)

    {   int child=DAG[x][i];

        retVal=max(retVal,dfs(child)+1);

    }

    dp[x]=retVal;

    return dp[x];

}

int main()

{

    cin>>n>>m;

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

    {

        int x,y;

        cin>>x>>y;

        DAG[x].push_back(y);

    }

    memset(dp,-1,sizeof(dp));

    int longestPath=0;

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

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



    cout << longestPath << endl;



    return 0;

}


// Faster C++ solution for the same problem (measured speedup: 2.097268579139362x):
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;



int dp[100001];

bool visited[100001];

vector<int> graph[100001];

int ans;

void dfs(int node){

    visited[node] = true;

    if(graph[node].empty()){ dp[node] = 0; return;}

    int maxa =0;

    for(auto i : graph[node]){

        if(!visited[i]){

            dfs(i);

        }

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

    }

    dp[node] = 1 + maxa;

}

int n, m;

int main(){

    cin>>n>>m;

    while(m--){

        int u, v;

        cin>>u>>v;

        graph[u].push_back(v);

    }

    int ans = 0;

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

        dfs(x);

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

    }

    cout<<ans;



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

#include <algorithm>

#include <iostream>

#include <iomanip>

#include <cstdio>

#include <cstdlib>

#include <cmath>

#include <cstring>

#include <vector>

#include <string>

#include <climits>

#include <map>

#include <set>

#include <stack>

#include <queue>

#include <deque>

#include <stdio.h>

//#define int long long

using namespace std;

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

#define endl '\n'

#define OnlineJudgec

#define F first

#define S second

#define  precision(n)  cout << fixed << setprecision(n)

#define clr(v,d ) memset(v, d, sizeof(v))

typedef long long ll;

typedef vector<int> vi;

void init()

{

    cin.tie(0);

    cin.sync_with_stdio(0);

    cout.tie(0);

    #ifdef OnlineJudge

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

    freopen("output.txt","w",stdout);

    #endif

}

ll S(ll x){ll s = 0;while(x){s += x % 10;x /= 10;}return s;} /// sum of digits.

ll powe(ll a , ll n){if(n == 1)return a;return a * powe(a ,n-1);}

ll com(int n,int m){ll z = 1;for(int i = 0; i < m;i++){z = z * ( n - i) / (i + 1) ;}return z;}

int dx[] = {1,-1,0,0};

int dy[] = {0,0,1,-1};

int dr[] = {0,0,0,1,1,1,-1,-1,-1};

int dc[] ={-1,0,1,-1,0,1,-1,0,1};

/// <<------------------------------------------------------------------------------>>

const int N = 100009;

int n,m;

int MOD = int(1e9) + 7;

int dp[N];

vector<vi>g(N);

int dfs(int node)

{

    int &rst = dp[node];

    if(~rst)

        return rst;

    rst  = 0;

    for(int neighbor : g[node])

    {

        rst =max(rst , 1 + dfs(neighbor));

    }

    return rst;

}

/// <<------------------------------------------------------------------------------>>

int main()

{

    init();

    clr(dp,-1);

    cin >> n >> m;

    loop(m)

    {

        int l ,r;

        cin >> l >> r;

        g[l].push_back(r);

    }

    int ans = 0;

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

    {

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

    }

    cout<<ans<<endl;

}


// Faster C++ solution for the same problem (measured speedup: 1.1318938027298846x):
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;



int dp[100001];

bool visited[100001];

vector<int> graph[100001];

int ans;

void dfs(int node){

    visited[node] = true;

    if(graph[node].empty()){ dp[node] = 0; return;}

    int maxa =0;

    for(auto i : graph[node]){

        if(!visited[i]){

            dfs(i);

        }

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

    }

    dp[node] = 1 + maxa;

}

int n, m;

int main(){

    cin>>n>>m;

    while(m--){

        int u, v;

        cin>>u>>v;

        graph[u].push_back(v);

    }

    int ans = 0;

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

        dfs(x);

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

    }

    cout<<ans;



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

using namespace std;

#define print printf("==================\n")

#define ll long long

#define pi acos(-1.0)

#define eps 1e-16

#define max3(a,b,c) max(a,max(b,c))

const ll INF = 1 << 30;

typedef pair<double, double  > payar;

typedef struct

{

    ll  x, y;

} point;

priority_queue<payar, vector<payar>,  greater<payar> > pq; ///accending

vector< pair<double,payar  > > vpp;

vector < payar >  vp;

vector<int>g[100005];

int ind[100005];

int vis[100005];

int dis[100005];



int dfs(int u)

{



    vis[u]=1;

    if(dis[u]!=-1)return dis[u];

    int maxi =0;

    for(auto it: g[u])

    {

       // static int k;

     //   cout<<k++<<" "<<it<<endl;



      dis[u]=  maxi=max(maxi,1+dfs(it) );

    }

    return maxi;

}

int main()

{



    int n, m ;

    cin>>n>>m;

    memset(dis,-1,sizeof dis);

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

    {

        int u, v;

        cin>>u>>v;

        g[u].push_back(v);

        ind[v]++;



    }

    int ans =0;

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

    {

        if(ind[i]==0 and vis[i]==0)

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

    }

    cout<<ans;

    return  0 ;

}


// Faster C++ solution for the same problem (measured speedup: 1.1044666330958277x):
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int maxN = 1e5 + 10;



int n, m;

vector<int> g[maxN];

int vis[maxN];

int dp[maxN];

stack<int> s;

vector<int> ver;



void dfs(int u) {

  s.push(u);

  vis[u] = 1;

  for (auto v : g[u]) {

    if (!vis[v]) dfs(v);

  }

  ver.push_back(u);

  s.pop();

}



int main(){

//  freopen("abc.inp", "r", stdin); freopen("abc.out", "w", stdout);

  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

  cin >> n >> m;

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

    int u, v; cin >> u >> v;

    g[u].push_back(v);

  }

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

    if (!vis[i]) {

      dfs(i);

    }

  }

  int ans = 0;

  for (int i = 0; i < ver.size(); ++i) {

    int u = ver[i];

    for (auto v : g[u]) {

      dp[u] = max(dp[u], dp[v] + 1);

    }

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

  }

  cout << ans;

return 0;

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

#define ll long long

using namespace std;

ll n,m,x,y;

vector<ll>v[100009];

ll dp[100009];



ll f(ll N){

	if (v[N].empty())return 0;

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

	ll z=0;

	for(int i=0; i<v[N].size(); i++){

		z=max(z,f(v[N][i])+1);

	}

	dp[N]=z;

	return dp[N];

}



int main(){

	cin >> n >> m;

	memset(dp,-1,sizeof dp);

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

		cin >> x >> y;

		v[x].push_back(y);

	}

	ll jwb=0;

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

		jwb=max(jwb,f(i));

	}

	cout << jwb << endl;

}

// Faster C++ solution for the same problem (measured speedup: 1.2283932866407974x):
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int maxN = 1e5 + 10;



int n, m;

vector<int> g[maxN];

int vis[maxN];

int dp[maxN];

stack<int> s;

vector<int> ver;



void dfs(int u) {

  s.push(u);

  vis[u] = 1;

  for (auto v : g[u]) {

    if (!vis[v]) dfs(v);

  }

  ver.push_back(u);

  s.pop();

}



int main(){

//  freopen("abc.inp", "r", stdin); freopen("abc.out", "w", stdout);

  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

  cin >> n >> m;

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

    int u, v; cin >> u >> v;

    g[u].push_back(v);

  }

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

    if (!vis[i]) {

      dfs(i);

    }

  }

  int ans = 0;

  for (int i = 0; i < ver.size(); ++i) {

    int u = ver[i];

    for (auto v : g[u]) {

      dp[u] = max(dp[u], dp[v] + 1);

    }

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

  }

  cout << ans;

return 0;

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

#define ll long long

using namespace std;

ll n,m,x,y;

vector<ll>v[100009];

ll dp[100009];



ll f(ll N){

	if (v[N].empty())return 0;

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

	ll z=0;

	for(int i=0; i<v[N].size(); i++){

		z=max(z,f(v[N][i])+1);

	}

	dp[N]=z;

	return dp[N];

}



int main(){

	cin >> n >> m;

	memset(dp,-1,sizeof dp);

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

		cin >> x >> y;

		v[x].push_back(y);

	}

	ll jwb=0;

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

		jwb=max(jwb,f(i));

	}

	cout << jwb << endl;

}//z

// Faster C++ solution for the same problem (measured speedup: 1.2283932866407974x):
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int maxN = 1e5 + 10;



int n, m;

vector<int> g[maxN];

int vis[maxN];

int dp[maxN];

stack<int> s;

vector<int> ver;



void dfs(int u) {

  s.push(u);

  vis[u] = 1;

  for (auto v : g[u]) {

    if (!vis[v]) dfs(v);

  }

  ver.push_back(u);

  s.pop();

}



int main(){

//  freopen("abc.inp", "r", stdin); freopen("abc.out", "w", stdout);

  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

  cin >> n >> m;

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

    int u, v; cin >> u >> v;

    g[u].push_back(v);

  }

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

    if (!vis[i]) {

      dfs(i);

    }

  }

  int ans = 0;

  for (int i = 0; i < ver.size(); ++i) {

    int u = ver[i];

    for (auto v : g[u]) {

      dp[u] = max(dp[u], dp[v] + 1);

    }

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

  }

  cout << ans;

return 0;

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





using namespace std;



vector<int> v[100005];

bool processado[100005];

int tab[100005];



int dfs(int s)

{



    //processado[s] = true;

    int soma, max = 0, entrou = 0;

    

    if(tab[s] >= 0)

    {

        return tab[s];

    }

    for (int i = 0; i < v[s].size(); ++i)

    {



        entrou = 1;

        soma = dfs(v[s][i]) + 1;

        if(soma > max)

        {

            max = soma;

            tab[s] = max;

        }

    }

    if(entrou == 1)

    {

        return max;

    }



    return tab[s] = 0;



}

 





int main(){



    int n, m;

    cin >> n >> m;

    memset(tab, -1, sizeof(tab));



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

    {

        processado[i] = false;

    }*/



    int x, y;

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

    {

        cin >> x >> y;

        v[x].push_back(y);

    }



    int soma = 0;

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

    {

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

    }



    cout << soma << endl;











    



    

    return 0;

}


// Faster C++ solution for the same problem (measured speedup: 1.102762393643043x):
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int maxN = 1e5 + 10;



int n, m;

vector<int> g[maxN];

int vis[maxN];

int dp[maxN];

stack<int> s;

vector<int> ver;



void dfs(int u) {

  s.push(u);

  vis[u] = 1;

  for (auto v : g[u]) {

    if (!vis[v]) dfs(v);

  }

  ver.push_back(u);

  s.pop();

}



int main(){

//  freopen("abc.inp", "r", stdin); freopen("abc.out", "w", stdout);

  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

  cin >> n >> m;

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

    int u, v; cin >> u >> v;

    g[u].push_back(v);

  }

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

    if (!vis[i]) {

      dfs(i);

    }

  }

  int ans = 0;

  for (int i = 0; i < ver.size(); ++i) {

    int u = ver[i];

    for (auto v : g[u]) {

      dp[u] = max(dp[u], dp[v] + 1);

    }

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

  }

  cout << ans;

return 0;

}