Problem: There is a directed graph G with N vertices and M edges. The vertices are numbered 1, 2, \ldots, N, and for each i (1 \leq i \leq M), the i-th directed edge goes from Vertex x_i to y_i. G does not contain directed cycles.

Find the length of the longest directed path in G. Here, the length of a directed path is the number of edges in it.

Constraints

* All values in input are integers.
* 2 \leq N \leq 10^5
* 1 \leq M \leq 10^5
* 1 \leq x_i, y_i \leq N
* All pairs (x_i, y_i) are distinct.
* G does not contain directed cycles.

Input

Input is given from Standard Input in the following format:


N M
x_1 y_1
x_2 y_2
:
x_M y_M


Output

Print the length of the longest directed path in G.

Examples

Input

4 5
1 2
1 3
3 2
2 4
3 4


Output

3


Input

6 3
2 3
4 5
5 6


Output

2


Input

5 8
5 3
2 3
2 4
5 2
5 1
1 4
4 3
1 3


Output

3

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;
int n, m, x, y, dp[100005];
vector<int>node[100005];
bool vis[100005];

int solve(int a){
	if(vis[a]){
		return dp[a];
	}
	vis[a]=1;
	int total=0;
	for(auto i:node[a]){
		total=max(total, 1+solve(i));
	}
	return dp[a]=total;
}

int main(){
	ios_base::sync_with_stdio(0);
	cin.tie();
	cout.tie();
	cin >> n >> m;
	for(int i=1;i<=m;i++){
		cin >> x >> y;
		node[x].push_back(y);
	}
	int ha=0;
	for(int i=1;i<=n;i++){
 	   ha=max(ha, solve(i));
	}
	cout << ha << endl;
}