stablegradients/pie-gem5-pairs huggingface dataset:
// Slower C++ solution:
#include<set>

#include<map>

#include<cmath>

#include<ctime>

#include<queue>

#include<stack>

#include<cstdio>

#include<string>

#include<vector>

#include<random>

#include<cstdlib>

#include<cstring>

#include<iomanip>

#include<iostream>

#include<algorithm>

#include<unordered_map>

#define endl "\n"

#define fi first

#define se second

#define db double

#define gcd __gcd

#define pb push_back

#define mp make_pair

#define lowbit(x) (x & (-x))

#define PII  pair<int, int> 

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

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

#define rep(i, a, b) for(__typeof(b) i = a; i <= (b); i++)

#define Rep(i, a, b) for(__typeof(a) i = a; i >= (b); i--)

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

template<class T> inline T qmin(T a, T b) { return a < b ? a : b; }

template<class T> inline T qmax(T a, T b) { return a > b ? a : b; }

typedef long long ll;

typedef unsigned long long ull;

const db eps = 1e-9;

const db PI = acos(-1);

const int inf = 0x3f3f3f3f;

const int mod = (int)1e9 + 7;

const int maxn = (int)1e5 + 5;//remember to modify it, No RE or MLE

const ll INF = 0x3f3f3f3f3f3f3f3f;

using namespace std;

ll qpow(ll x, ll y) { ll ret = 1; for( ; y; y >>= 1, x = (x * x) % mod) if(y & 1) ret = (ret * x) % mod; return ret; }



inline int read(){

	char ch = getchar();

	int x = 0, f = 1;

	while(ch < '0' || ch > '9'){

		if(ch == '-') f = -1;

		ch = getchar();

	}

	while('0' <= ch && ch <= '9'){

		x = x * 10 + ch - '0';

		ch = getchar();

	}

	return x * f;

}



int n, m;

vector<int> G[maxn];

int dp[maxn], ind[maxn];



void dfs(int u){

	for(int v : G[u]){

		if(!dp[v]){

			dfs(v);

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

		} else {

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

		}

	}

}



int main()

{

	n = read(), m = read();

	rep(i, 1, m) {

		int u = read(), v = read();

		G[u].pb(v);

		ind[v]++;

	}

	rep(i, 1, n){

		if(!ind[i]){

			dfs(i);

		}

	}

	printf("%d\n", *max_element(dp, dp + n + 1));

	return 0;

}

// Faster C++ solution for the same problem (measured speedup: 3.5107984456409813x):
#include <iostream>

#include <algorithm>

#include <vector>



std::vector<std::vector<int>> vec;

std::vector<int> dp;



int dfs(int node)

{

	if (vec[node].empty())

		return 0;

	if (dp[node] != -1)

		return dp[node];

	int max = 0;

	for (int i : vec[node])

	{

		int temp = dfs(i);

		dp[i] = temp;

		max = std::max(max, temp);

	}

	return max + 1;

}



int main()

{

	int n, m;

	std::cin >> n >> m;

	vec = std::vector<std::vector<int>>(n + 1);

	dp = std::vector<int>(n + 1, -1);

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

	{

		int x, y;

		std::cin >> x >> y;

		vec[x].push_back(y);

	}

	int max = 0;

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

		max = std::max(max, dfs(i));

	std::cout << max << '\n';

	return 0;

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

#include<queue>

#include<vector>

#define ii pair<int,int>

#define iii pair<int,ii> 

using namespace std;

int v,e,a,b;

vector<int> adjl[110000];

int vis[110000];

int memo[110000];

int start = 0;

int dp(int nodes){

//	cout<<nodes<<"\n";

	int sz = adjl[nodes].size();

	if(sz == 0) return 0;

	if(memo[nodes]!=-1) return memo[nodes];

	int ret = 0;

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

//		cout<<" visit "<<adjl[nodes][i]<<"\n";

		ret = max(ret, dp(adjl[nodes][i]) + 1);

	}

//	cout<<"\n";

	return memo[nodes] = ret;

}





int main(){

	cin>>v>>e;

	for(int i = 1;i<=v;i++) adjl[0].push_back(i);

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

		cin>>a>>b;

		adjl[a].push_back(b);

	}

	int ans = 0;

	for(int i = 0;i<=v;i++) memo[i] = -1;

	ans = dp(0) -1 ;

	cout<<ans<<"\n";

//	for(int i = 0;i<=v;i++) cout<<memo[i]<<" ";cout<<"\n";

//	for(int i = 0;i<=v;i++) ans = max(ans,)

	return 0;

}

// Faster C++ solution for the same problem (measured speedup: 3.7884356175350478x):
#include <iostream>

#include <algorithm>

#include <vector>



std::vector<std::vector<int>> vec;

std::vector<int> dp;



int dfs(int node)

{

	if (vec[node].empty())

		return 0;

	if (dp[node] != -1)

		return dp[node];

	int max = 0;

	for (int i : vec[node])

	{

		int temp = dfs(i);

		dp[i] = temp;

		max = std::max(max, temp);

	}

	return max + 1;

}



int main()

{

	int n, m;

	std::cin >> n >> m;

	vec = std::vector<std::vector<int>>(n + 1);

	dp = std::vector<int>(n + 1, -1);

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

	{

		int x, y;

		std::cin >> x >> y;

		vec[x].push_back(y);

	}

	int max = 0;

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

		max = std::max(max, dfs(i));

	std::cout << max << '\n';

	return 0;

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

using namespace std;

const int N = 1e5 + 10;

int n, m, dp[N];

vector<int> gg[N];

int dfs(int v){

	if (gg[v].size() == 0 || dp[v] != 0){

		return dp[v];

	}

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

		int child = gg[v][i];

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

	}

	return dp[v];

}

int main(){

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

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

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

	// cout << setprecision(10) << fixed;

	cin>>n>>m;

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

		int from, to;

		cin>>from>>to;

		gg[from].push_back(to);

	}

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

		dfs(i);

	}

	int ans = 0;

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

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

	}

	cout<<ans;

}

// Faster C++ solution for the same problem (measured speedup: 3.549533051160695x):
#include <iostream>

#include <algorithm>

#include <vector>



std::vector<std::vector<int>> vec;

std::vector<int> dp;



int dfs(int node)

{

	if (vec[node].empty())

		return 0;

	if (dp[node] != -1)

		return dp[node];

	int max = 0;

	for (int i : vec[node])

	{

		int temp = dfs(i);

		dp[i] = temp;

		max = std::max(max, temp);

	}

	return max + 1;

}



int main()

{

	int n, m;

	std::cin >> n >> m;

	vec = std::vector<std::vector<int>>(n + 1);

	dp = std::vector<int>(n + 1, -1);

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

	{

		int x, y;

		std::cin >> x >> y;

		vec[x].push_back(y);

	}

	int max = 0;

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

		max = std::max(max, dfs(i));

	std::cout << max << '\n';

	return 0;

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

#include <vector>

#include <queue>



using namespace std;

struct snod

{

    vector <int> v;

    int len,leg;

} nod[100005];

int n,m,i,x,y,maxi;

queue <int> q;

int main()

{

    cin>>n>>m;

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

    {

        cin>>x>>y;

        nod[x].v.push_back(y);

        nod[y].leg++;

    }

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

        if(!nod[i].leg)

        {

            q.push(i);

        }



    while(!q.empty())

    {

        int poz=q.front();

        for(int it : nod[poz].v)

        {

            nod[it].len=max(nod[it].len, nod[poz].len+1);

            nod[it].leg--;

            if(!nod[it].leg)

                q.push(it);

        }

        q.pop();

    }

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

    {

        maxi=max(maxi, nod[i].len);

    }

    cout<<maxi;

    return 0;

}


// Faster C++ solution for the same problem (measured speedup: 4.342755955021119x):
#include <iostream>

#include <algorithm>

#include <vector>



std::vector<std::vector<int>> vec;

std::vector<int> dp;



int dfs(int node)

{

	if (vec[node].empty())

		return 0;

	if (dp[node] != -1)

		return dp[node];

	int max = 0;

	for (int i : vec[node])

	{

		int temp = dfs(i);

		dp[i] = temp;

		max = std::max(max, temp);

	}

	return max + 1;

}



int main()

{

	int n, m;

	std::cin >> n >> m;

	vec = std::vector<std::vector<int>>(n + 1);

	dp = std::vector<int>(n + 1, -1);

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

	{

		int x, y;

		std::cin >> x >> y;

		vec[x].push_back(y);

	}

	int max = 0;

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

		max = std::max(max, dfs(i));

	std::cout << max << '\n';

	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: 7.464350258632975x):
#include <iostream>

#include <algorithm>

#include <vector>



std::vector<std::vector<int>> vec;

std::vector<int> dp;



int dfs(int node)

{

	if (vec[node].empty())

		return 0;

	if (dp[node] != -1)

		return dp[node];

	int max = 0;

	for (int i : vec[node])

	{

		int temp = dfs(i);

		dp[i] = temp;

		max = std::max(max, temp);

	}

	return max + 1;

}



int main()

{

	int n, m;

	std::cin >> n >> m;

	vec = std::vector<std::vector<int>>(n + 1);

	dp = std::vector<int>(n + 1, -1);

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

	{

		int x, y;

		std::cin >> x >> y;

		vec[x].push_back(y);

	}

	int max = 0;

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

		max = std::max(max, dfs(i));

	std::cout << max << '\n';

	return 0;

}
// 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: 3.9294256943516346x):
#include <iostream>

#include <algorithm>

#include <vector>



std::vector<std::vector<int>> vec;

std::vector<int> dp;



int dfs(int node)

{

	if (vec[node].empty())

		return 0;

	if (dp[node] != -1)

		return dp[node];

	int max = 0;

	for (int i : vec[node])

	{

		int temp = dfs(i);

		dp[i] = temp;

		max = std::max(max, temp);

	}

	return max + 1;

}



int main()

{

	int n, m;

	std::cin >> n >> m;

	vec = std::vector<std::vector<int>>(n + 1);

	dp = std::vector<int>(n + 1, -1);

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

	{

		int x, y;

		std::cin >> x >> y;

		vec[x].push_back(y);

	}

	int max = 0;

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

		max = std::max(max, dfs(i));

	std::cout << max << '\n';

	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: 1.8408941237320284x):


#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;

}
// 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: 1.2341136498463032x):


#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;

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

#include <vector>

#include <queue>



using namespace std;

struct snod

{

    vector <int> v;

    int len,leg;

} nod[100005];

int n,m,i,x,y,maxi;

queue <int> q;

int main()

{

    cin>>n>>m;

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

    {

        cin>>x>>y;

        nod[x].v.push_back(y);

        nod[y].leg++;

    }

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

        if(!nod[i].leg)

        {

            q.push(i);

        }



    while(!q.empty())

    {

        int poz=q.front();

        for(int it : nod[poz].v)

        {

            nod[it].len=max(nod[it].len, nod[poz].len+1);

            nod[it].leg--;

            if(!nod[it].leg)

                q.push(it);

        }

        q.pop();

    }

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

    {

        maxi=max(maxi, nod[i].len);

    }

    cout<<maxi;

    return 0;

}


// Faster C++ solution for the same problem (measured speedup: 1.231127418660571x):


#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;

}
// 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: 2.116067852089213x):


#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;

}
// 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: 1.1139524675137134x):


#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;

}
// 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: 1.8408941237320284x):
#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;

}
// 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: 1.2341136498463032x):
#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;

}