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

using namespace std;

vector<int>adj[100005];

int dp[100005];

bool vis[100005];

void dfs(int u)

{

    vis[u]=true;

    for(auto v:adj[u])

    {

        if(vis[v]==false)

            dfs(v);

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

    }





}

int main()

{

    int n,m;

    cin>>n>>m;

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

    {

        int u,v;

        cin>>u>>v;

        adj[u].push_back(v);

    }

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

    {

        if(vis[i]==false)

            dfs(i);

    }

    int ans=0;

    for(int i=1; i<=n; i++) ans=max(ans,dp[i]);

    cout<<ans<<endl;

}


// Faster C++ solution for the same problem (measured speedup: 3.4550485764337124x):
#include <bits/stdc++.h>

#define ll          long long int

#define pii         pair<int,int>

#define uu          first

#define vv          second

#define fastIO      ios::sync_with_stdio(0);cin.tie(0);

using namespace std;



const int MAX = 2e5 + 5;

const ll INF = 1e18;

int main()

{

    fastIO;

    int n, m;

    cin>>n>>m;

    

    vector< vector<int> >edg(n+1), rev(n+1);

    vector<int>deg(n+1), dp(n+1);

    

    while(m--) {

        

        int u , v;

        cin>>u>>v;

        edg[u].push_back(v);

        rev[v].push_back(u);

        deg[u]++;

    }

    

    queue<int>q;

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

        if(deg[i] == 0) q.push(i);

    }

    int ans = 0;

    

    while(!q.empty()) {

        

        int top = q.front();

        q.pop();

        for(auto x : edg[top]) dp[top] = max(dp[top] , dp[x] + 1);

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

        for(auto x : rev[top]) {

            deg[x]--;

            if(deg[x] == 0 ) q.push(x);

        }

    }

    cout<<ans<<'\n';

    return 0;

}
// Slower C++ solution:
/*

██╗  ██╗ █████╗ ██████╗ ███████╗███████╗███╗   ███╗        ██╗  ██╗██╗  ██╗ █████╗ ██╗     ███████╗██████╗

██║ ██╔╝██╔══██╗██╔══██╗██╔════╝██╔════╝████╗ ████║        ██║ ██╔╝██║  ██║██╔══██╗██║     ██╔════╝██╔══██╗

█████╔╝ ███████║██████╔╝█████╗  █████╗  ██╔████╔██║        █████╔╝ ███████║███████║██║     █████╗  ██║  ██║

██╔═██╗ ██╔══██║██╔══██╗██╔══╝  ██╔══╝  ██║╚██╔╝██║        ██╔═██╗ ██╔══██║██╔══██║██║     ██╔══╝  ██║  ██║

██║  ██╗██║  ██║██║  ██║███████╗███████╗██║ ╚═╝ ██║███████╗██║  ██╗██║  ██║██║  ██║███████╗███████╗██████╔╝

╚═╝  ╚═╝╚═╝  ╚═╝╚═╝  ╚═╝╚══════╝╚══════╝╚═╝     ╚═╝╚══════╝╚═╝  ╚═╝╚═╝  ╚═╝╚═╝  ╚═╝╚══════╝╚══════╝╚═════╝

Believe in yourself ,( try and try and then try ), You can do it

*/

#define _CRT_SECURE_NO_WARNINGS

#include<bits/stdc++.h>

#include<unordered_map>

#define endl "\n"

#define Ceil(x,y) ((x+y-1)/y)

#define clr(arr, x) memset(arr, x, sizeof arr)

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

#define allr(s) s.rbegin(),s.rend()

#define rt(s) return cout<<s,0

#define watch(x) cout<<(#x)<<" = "<<x<<endl

#define sz(s)	(int)(s.size())

#define OO 0x3f3f3f3f3f3f3f3fLL

const int oo = 0x3f3f3f3f, mod = 1e9 + 7;

using namespace std;

typedef long long ll;

typedef long double ld;

typedef unsigned long long ull;

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

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

void K_K(){ 

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

}

vector<vector<int>>gr;

int dp[100005];

int dfs(int node){

	if (!sz(gr[node]))

		return 0;

	int &ret = dp[node];

	if (~ret)

		return ret;

	for (auto child : gr[node]){

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

	}

	return ret;

}

int main(){

	K_K();

	int n, m;

	cin >> n >> m;

	gr.resize(n + 1);

	clr(dp, -1);

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

		int u, v;

		cin >> u >> v;

		gr[u].push_back(v);

	}

	int ans = 0;

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

		dfs(i);

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

	}

	cout << ans;

}

// Faster C++ solution for the same problem (measured speedup: 1.3814616031031148x):
#include <bits/stdc++.h>

#define ll          long long int

#define pii         pair<int,int>

#define uu          first

#define vv          second

#define fastIO      ios::sync_with_stdio(0);cin.tie(0);

using namespace std;



const int MAX = 2e5 + 5;

const ll INF = 1e18;

int main()

{

    fastIO;

    int n, m;

    cin>>n>>m;

    

    vector< vector<int> >edg(n+1), rev(n+1);

    vector<int>deg(n+1), dp(n+1);

    

    while(m--) {

        

        int u , v;

        cin>>u>>v;

        edg[u].push_back(v);

        rev[v].push_back(u);

        deg[u]++;

    }

    

    queue<int>q;

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

        if(deg[i] == 0) q.push(i);

    }

    int ans = 0;

    

    while(!q.empty()) {

        

        int top = q.front();

        q.pop();

        for(auto x : edg[top]) dp[top] = max(dp[top] , dp[x] + 1);

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

        for(auto x : rev[top]) {

            deg[x]--;

            if(deg[x] == 0 ) q.push(x);

        }

    }

    cout<<ans<<'\n';

    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;

}//j

// Faster C++ solution for the same problem (measured speedup: 1.1047999881636352x):
#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, int pr){



    auto &ret = dp[node];

    if(ret!=-1) return ret;

    ret = 0;

    for(auto i: g[node]){

        if(i==pr) continue;

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

    }



    return ret;

}



void read(){



    int i,edge;

    memset(dp,-1,sizeof dp);

    cin>>N>>edge;

    for(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,0) );

    }



    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;

#define ll long long

#define ull unsigned long long

#define mst(a, b) memset((a), (b), sizeof(a))

#define mp(a, b) make_pair(a, b)

#define pi acos(-1)

#define pii pair<int, int>

#define pb push_back

const int INF = 0x3f3f3f3f;

const double eps = 1e-10;

const int maxn = 1e5 + 7;

const int maxm = 5e5 + 10;

const int mod = 1e9 + 7;

vector<int> s[maxn];

int vis[maxn];

int dp[maxn];

int main()

{

    ios::sync_with_stdio(0);

    cin.tie(0);

    cout.tie(0);

    mst(vis, 0);

    mst(dp, 0);

    queue<int> q;

    int n, m;

    cin >> n >> m;

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

    {

        int x, y;

        cin >> x >> y;

        vis[y]++;

        s[x].pb(y);

    }

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

    {

        if (!vis[i])

            q.push(i);

    }

    while (!q.empty())

    {

        int now = q.front();

        q.pop();

        int len = s[now].size();

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

        {

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

            vis[s[now][i]]--;

            if (vis[s[now][i]] == 0)

                q.push(s[now][i]);

        }

    }

    int ans = 0;

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

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

    cout << ans << endl;

    return 0;

}

// Faster C++ solution for the same problem (measured speedup: 1.1168626658737288x):
#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, int pr){



    auto &ret = dp[node];

    if(ret!=-1) return ret;

    ret = 0;

    for(auto i: g[node]){

        if(i==pr) continue;

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

    }



    return ret;

}



void read(){



    int i,edge;

    memset(dp,-1,sizeof dp);

    cin>>N>>edge;

    for(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,0) );

    }



    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:
// Author : Syed Mujtaba

// Seek knowledge from the Cradle to the Grave !!

// https://www.linkedin.com/in/syed-mujtaba-064a5016a 



#include <bits/stdc++.h>

using namespace std;

#define int     long long

#define fast_io ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);

#define mod ((int)(1e9 + 7))

vector < int > to[100005];

vector < int > from[100005];

vector < int > roots;

int dp[100005];

int cal(int i)

{

	if(dp[i] != -1)

		return dp[i];

	int dist = -1;

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

	{

		dist = max(dist, 1 + cal(to[i][j]));

	}

	return dp[i] = dist;

}

signed main()

{

	fast_io

	int n, m;

	int x, y;

	cin >> n >> m;

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

	{	

		cin >> x >> y;

		to[y].push_back(x);

		from[x].push_back(y);

	}

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

		dp[i] = -1;

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

	{

		if(to[i].size() == 0)

		{

			roots.push_back(i);

			dp[i] = 0;

		}

	}

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

	{

		if(dp[i] == -1)

			dp[i] = cal(i);

	}

	int ans = -1;

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

	{

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

	}

	cout << ans << endl;

}

// Faster C++ solution for the same problem (measured speedup: 1.622262847182082x):
#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, int pr){



    auto &ret = dp[node];

    if(ret!=-1) return ret;

    ret = 0;

    for(auto i: g[node]){

        if(i==pr) continue;

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

    }



    return ret;

}



void read(){



    int i,edge;

    memset(dp,-1,sizeof dp);

    cin>>N>>edge;

    for(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,0) );

    }



    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>

#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;

}//j

// Faster C++ solution for the same problem (measured speedup: 4.341022090207988x):
#include<bits/stdc++.h>

#define si(a) scanf("%d", &a)

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

using namespace std;

typedef long long ll;

typedef pair<int,int> pi;

typedef vector<int> vi;

vector<vector<int> > gr;

vi out;

vi ans;

vector<bool> visited;

vi aux;

void dfs(int u){

	visited[u] = true;

	//ans[u] = max(ans[u], val);

	fore(j,0,gr[u].size()){

		if(!visited[ gr[u][j] ])

			dfs(gr[u][j]);

		//ans[u] = max(ans[u], ans[ gr[u][j] ] + 1);

	}

	aux.push_back(u);

}

void solve(){

	int n,m;

	si(n); si(m);

	int x,y;

	gr.assign(n+1,vector<int>());

	out.assign(n+1,0);

	ans.assign(n+1,0);

	vector<pi> inv(m);

	aux.reserve(n);

	vi in(n+1);

	visited.assign(n+1,false);

	fore(i,0,m){

		si(x);si(y);

		inv[i] = pi(x,y);

		out[x]++;

		in[y]++;

	}

	fore(i,1,n+1)

		gr[i].reserve( in[i] );

	fore(i,0,m){

		x = inv[i].first;

		y = inv[i].second;

		gr[x].push_back(y);

	}

		

	fore(i,1,n+1)

		if(!visited[i])

			dfs(i);

	vi dp(n+1);

	//printf("aux: ");for(int i:aux) printf("%d ", i);printf("\n");

	for(int v: aux){

		if(gr[v].size() == 0)

			dp[v] = 0;

		else{

			int k = 0;

			for(int u: gr[v])

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

			dp[v] = k+1;

		}

	}

	int anss = 0;

	//printf("dp: ");for(int i:dp) printf("%d ", i);printf("\n");

	

	for(int i: dp)

		anss = max(anss, i);

	

	printf("%d\n", anss);

}

int main(){

	solve();

	return 0;

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



using namespace std;



#define ll long long int



int memo[(int)1e5 + 1];

vector<int> adj[(int)1e5 + 1];



bool vis[(int)1e5 + 1];



int dfs(int x) {

	

	if(vis[x])return memo[x];



	vis[x] = true;

	

	int temp = 1;



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

		memo[x] = max(memo[x], temp + dfs(adj[x][i]));

	}



	return memo[x];

}



int main() {



	ios_base::sync_with_stdio(0);

	cin.tie(0);

	

	int n,m; cin >> n >> m;

	int s,t;

	

	while(m--) {

		cin >> s >> t;

		adj[s].push_back(t);

	}



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

		dfs(i);

	}



	int ans = 0;

	

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

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

	}



	cout << ans << '\n';



	return 0;

}

// Faster C++ solution for the same problem (measured speedup: 3.5266449384913634x):
#include<bits/stdc++.h>

#define si(a) scanf("%d", &a)

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

using namespace std;

typedef long long ll;

typedef pair<int,int> pi;

typedef vector<int> vi;

vector<vector<int> > gr;

vi out;

vi ans;

vector<bool> visited;

vi aux;

void dfs(int u){

	visited[u] = true;

	//ans[u] = max(ans[u], val);

	fore(j,0,gr[u].size()){

		if(!visited[ gr[u][j] ])

			dfs(gr[u][j]);

		//ans[u] = max(ans[u], ans[ gr[u][j] ] + 1);

	}

	aux.push_back(u);

}

void solve(){

	int n,m;

	si(n); si(m);

	int x,y;

	gr.assign(n+1,vector<int>());

	out.assign(n+1,0);

	ans.assign(n+1,0);

	vector<pi> inv(m);

	aux.reserve(n);

	vi in(n+1);

	visited.assign(n+1,false);

	fore(i,0,m){

		si(x);si(y);

		inv[i] = pi(x,y);

		out[x]++;

		in[y]++;

	}

	fore(i,1,n+1)

		gr[i].reserve( in[i] );

	fore(i,0,m){

		x = inv[i].first;

		y = inv[i].second;

		gr[x].push_back(y);

	}

		

	fore(i,1,n+1)

		if(!visited[i])

			dfs(i);

	vi dp(n+1);

	//printf("aux: ");for(int i:aux) printf("%d ", i);printf("\n");

	for(int v: aux){

		if(gr[v].size() == 0)

			dp[v] = 0;

		else{

			int k = 0;

			for(int u: gr[v])

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

			dp[v] = k+1;

		}

	}

	int anss = 0;

	//printf("dp: ");for(int i:dp) printf("%d ", i);printf("\n");

	

	for(int i: dp)

		anss = max(anss, i);

	

	printf("%d\n", anss);

}

int main(){

	solve();

	return 0;

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

using namespace std;



const int N = 1e5 + 100;





#define mp make_pair

#define f first

#define s second



#define pb push_back



void boost()

{

	ios_base::sync_with_stdio(0);

	cin.tie(0);

	cout.tie(0);

}



int n,m;



vector<int>g[N];



bool was[N];



int d[N];



vector<int>ord;

int ans;



void dfs(int v)

{

 	was[v] = 1;

 	for (int to :g[v])

 	{

 		if (!was[to])

 		{

 			dfs(to);

 		}

 	}

 	ord.pb(v);

}

                                                                                                          

void dfs1(int v)

{

 	was[v] = 1;

 	for (int to :g[v])

 	{

 		if (!was[to])

 		{

 			dfs1(to);

 		}                               

 		d[v] = max(d[v],d[to] + 1);

 		ans = max(ans,d[v]);

 	}                          

}





int main(){

	boost();

	cin >> n >> m;

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

	{

		int u,v;

		cin >> u >> v;

		g[u].pb(v);

	}

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

	{

		if (!was[i])

		{             

			dfs(i);

		}

	}

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

	{

		was[i] = 0;

	}

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

	{                        

		dfs1(ord[i]);            

	}

	cout << ans;       

}

// Faster C++ solution for the same problem (measured speedup: 3.526648115964216x):
#include<bits/stdc++.h>

#define si(a) scanf("%d", &a)

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

using namespace std;

typedef long long ll;

typedef pair<int,int> pi;

typedef vector<int> vi;

vector<vector<int> > gr;

vi out;

vi ans;

vector<bool> visited;

vi aux;

void dfs(int u){

	visited[u] = true;

	//ans[u] = max(ans[u], val);

	fore(j,0,gr[u].size()){

		if(!visited[ gr[u][j] ])

			dfs(gr[u][j]);

		//ans[u] = max(ans[u], ans[ gr[u][j] ] + 1);

	}

	aux.push_back(u);

}

void solve(){

	int n,m;

	si(n); si(m);

	int x,y;

	gr.assign(n+1,vector<int>());

	out.assign(n+1,0);

	ans.assign(n+1,0);

	vector<pi> inv(m);

	aux.reserve(n);

	vi in(n+1);

	visited.assign(n+1,false);

	fore(i,0,m){

		si(x);si(y);

		inv[i] = pi(x,y);

		out[x]++;

		in[y]++;

	}

	fore(i,1,n+1)

		gr[i].reserve( in[i] );

	fore(i,0,m){

		x = inv[i].first;

		y = inv[i].second;

		gr[x].push_back(y);

	}

		

	fore(i,1,n+1)

		if(!visited[i])

			dfs(i);

	vi dp(n+1);

	//printf("aux: ");for(int i:aux) printf("%d ", i);printf("\n");

	for(int v: aux){

		if(gr[v].size() == 0)

			dp[v] = 0;

		else{

			int k = 0;

			for(int u: gr[v])

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

			dp[v] = k+1;

		}

	}

	int anss = 0;

	//printf("dp: ");for(int i:dp) printf("%d ", i);printf("\n");

	

	for(int i: dp)

		anss = max(anss, i);

	

	printf("%d\n", anss);

}

int main(){

	solve();

	return 0;

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

/**

*   author: j o s e m a g o

*   date:

**/

using namespace std;

#pragma GCC optimize ("Ofast")

#define f first

#define s second

#define mp make_pair

#define lb lower_bound

#define ub upper_bound

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

#define mset(a,v) memset(a,v,sizeof(a))

#define pb push_back

#define sz(x) ((int)(x).size())

#define rsz resize

#define ln "\n"



typedef double db;

typedef unsigned long long ull;

typedef long long ll;

typedef long double ld;

const ld PI = 2*acos(0.0);

const int MOD = 1000000007;

const int JJJ = 100009;



int N,A;

vector<int>grafo[JJJ];

bool visited[JJJ];

int dp[JJJ];



int sol = 0;

void dfs(int nod){

    visited[nod] = true;

    dp[nod] = -1;

    for(int i = 0;i < (int)grafo[nod].size();i++){

        int xx = grafo[nod][i];

        if(!visited[xx]){

            dfs(xx);

        }

        dp[nod] = max(dp[nod],dp[xx]);

    }

    dp[nod]++;

}







int main(){



  

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





    cin >> N >> A;

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

        int a,b;

        cin >> a >> b;

        grafo[a].pb(b);

    }



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

        if(!visited[i]){

            dfs(i);

        }

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

    }



    cout<<sol;







    return 0;

}

// Faster C++ solution for the same problem (measured speedup: 3.5248427987115085x):
#include<bits/stdc++.h>

#define si(a) scanf("%d", &a)

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

using namespace std;

typedef long long ll;

typedef pair<int,int> pi;

typedef vector<int> vi;

vector<vector<int> > gr;

vi out;

vi ans;

vector<bool> visited;

vi aux;

void dfs(int u){

	visited[u] = true;

	//ans[u] = max(ans[u], val);

	fore(j,0,gr[u].size()){

		if(!visited[ gr[u][j] ])

			dfs(gr[u][j]);

		//ans[u] = max(ans[u], ans[ gr[u][j] ] + 1);

	}

	aux.push_back(u);

}

void solve(){

	int n,m;

	si(n); si(m);

	int x,y;

	gr.assign(n+1,vector<int>());

	out.assign(n+1,0);

	ans.assign(n+1,0);

	vector<pi> inv(m);

	aux.reserve(n);

	vi in(n+1);

	visited.assign(n+1,false);

	fore(i,0,m){

		si(x);si(y);

		inv[i] = pi(x,y);

		out[x]++;

		in[y]++;

	}

	fore(i,1,n+1)

		gr[i].reserve( in[i] );

	fore(i,0,m){

		x = inv[i].first;

		y = inv[i].second;

		gr[x].push_back(y);

	}

		

	fore(i,1,n+1)

		if(!visited[i])

			dfs(i);

	vi dp(n+1);

	//printf("aux: ");for(int i:aux) printf("%d ", i);printf("\n");

	for(int v: aux){

		if(gr[v].size() == 0)

			dp[v] = 0;

		else{

			int k = 0;

			for(int u: gr[v])

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

			dp[v] = k+1;

		}

	}

	int anss = 0;

	//printf("dp: ");for(int i:dp) printf("%d ", i);printf("\n");

	

	for(int i: dp)

		anss = max(anss, i);

	

	printf("%d\n", anss);

}

int main(){

	solve();

	return 0;

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

using namespace std;

const int N = 1e5 + 25, M = 1e6 + 25, oo = 1e9, mod = 1e9 + 7;

const long long OO = 1e18+25;



int n, m,u,v, mx, mem[N];

vector <int> g[N];



int dp(int p)

{

    int &ret = mem[p];

    if(ret != 0) return ret;

    for(int to : g[p])

        ret = max(ret, dp(to)+1);

    return ret;

}



int main()

{

    scanf("%d%d",&n,&m);

    while(m--)

    {

        scanf("%d%d",&u,&v);

        g[u].push_back(v);

    }

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

    {

        mx = max(mx, dp(i));

    }

    printf("%d\n",mx);

    return 0;

}

	     		 					   	 	 								 	

// Faster C++ solution for the same problem (measured speedup: 3.4891025045614144x):
#include<bits/stdc++.h>

#define si(a) scanf("%d", &a)

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

using namespace std;

typedef long long ll;

typedef pair<int,int> pi;

typedef vector<int> vi;

vector<vector<int> > gr;

vi out;

vi ans;

vector<bool> visited;

vi aux;

void dfs(int u){

	visited[u] = true;

	//ans[u] = max(ans[u], val);

	fore(j,0,gr[u].size()){

		if(!visited[ gr[u][j] ])

			dfs(gr[u][j]);

		//ans[u] = max(ans[u], ans[ gr[u][j] ] + 1);

	}

	aux.push_back(u);

}

void solve(){

	int n,m;

	si(n); si(m);

	int x,y;

	gr.assign(n+1,vector<int>());

	out.assign(n+1,0);

	ans.assign(n+1,0);

	vector<pi> inv(m);

	aux.reserve(n);

	vi in(n+1);

	visited.assign(n+1,false);

	fore(i,0,m){

		si(x);si(y);

		inv[i] = pi(x,y);

		out[x]++;

		in[y]++;

	}

	fore(i,1,n+1)

		gr[i].reserve( in[i] );

	fore(i,0,m){

		x = inv[i].first;

		y = inv[i].second;

		gr[x].push_back(y);

	}

		

	fore(i,1,n+1)

		if(!visited[i])

			dfs(i);

	vi dp(n+1);

	//printf("aux: ");for(int i:aux) printf("%d ", i);printf("\n");

	for(int v: aux){

		if(gr[v].size() == 0)

			dp[v] = 0;

		else{

			int k = 0;

			for(int u: gr[v])

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

			dp[v] = k+1;

		}

	}

	int anss = 0;

	//printf("dp: ");for(int i:dp) printf("%d ", i);printf("\n");

	

	for(int i: dp)

		anss = max(anss, i);

	

	printf("%d\n", anss);

}

int main(){

	solve();

	return 0;

}