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;
typedef long long ll;
#define pb push_back
#define mp make_pair
int dp[100010]={0};
unordered_map<int,vector<int>>nodes;
int cal(int i){
if(dp[i]!=0)return dp[i];
int &x=dp[i];
for(auto j:nodes[i])x=max(1+ cal(j),x);
return dp[i]=x;
}
int main(){
int n,m;
cin>>n>>m;
for(int i=0;i<m;i++){
    int x,y;
    cin>>x>>y;
    nodes[x].pb(y);
}
int is=0;
for(int i=1;i<=n;i++){
    is=max(is,cal(i));
}
cout<<is<<'\n';
return 0;
}