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
#include<bits/stdc++.h>
using namespace std;
const int N=1e5+5;
bool visi[N];
vector<int>adj[N];
int dis[N];
void dfs(int s)
{
   visi[s]=1;
for(int i=0;i<adj[s].size();i++)
{
if(visi[adj[s][i]]==0)
dfs(adj[s][i]);
dis[s]=max(dis[s],dis[adj[s][i]]+1);
}
}
int  main()
{
  int n,m;
cin>>n>>m;
for(int i=0;i<m;i++)
{
int x,y;
cin>>x>>y;
adj[x].push_back(y);
}
for(int i=1;i<=n;i++)
if(visi[i]==0)
dfs(i);
int ma=0;
for(int i=1;i<=n;i++)
ma=max(dis[i],ma);
cout<<ma<<endl;
}
