Further research on zombie thought processes yielded interesting results. As we know from the previous problem, the nervous system of a zombie consists of n brains and m brain connectors joining some pairs of brains together. It was observed that the intellectual abilities of a zombie depend mainly on the topology of its nervous system. More precisely, we define the distance between two brains u and v (1 ≤ u, v ≤ n) as the minimum number of brain connectors used when transmitting a thought between these two brains. The brain latency of a zombie is defined to be the maximum distance between any two of its brains. Researchers conjecture that the brain latency is the crucial parameter which determines how smart a given zombie is. Help them test this conjecture by writing a program to compute brain latencies of nervous systems.

In this problem you may assume that any nervous system given in the input is valid, i.e., it satisfies conditions (1) and (2) from the easy version.

Input

The first line of the input contains two space-separated integers n and m (1 ≤ n, m ≤ 100000) denoting the number of brains (which are conveniently numbered from 1 to n) and the number of brain connectors in the nervous system, respectively. In the next m lines, descriptions of brain connectors follow. Every connector is given as a pair of brains a b it connects (1 ≤ a, b ≤ n and a ≠ b).

Output

Print one number – the brain latency.

Examples

Input

4 3
1 2
1 3
1 4


Output

2

Input

5 4
1 2
2 3
3 4
3 5


Output

3
//package Practice_Problems;
import java.util.*;
import java.io.*;
public class C2
{
	static ArrayList<Integer> adj[] = new ArrayList[(int) 1e5 + 1];
	static boolean vis[]=new boolean[adj.length];
	static int max_dist=0,max_node=0;
	static final int mod=(int)1e9+7;
	static final int inf=(int)1e9;
	static final long INF=(long)1e18;
	public static void main(String[] args) throws IOException
	{
		FastScanner fs=new FastScanner();
		PrintWriter out = new PrintWriter(System.out);
		int nodes=fs.nextInt();int edges=fs.nextInt();
		for(int i=1;i<=nodes;i++)adj[i]=new ArrayList<Integer>();
		for(int i=1;i<=edges;i++)
		{
			int a=fs.nextInt();int b=fs.nextInt();
			adj[a].add(b);adj[b].add(a);
		}
		dfs(1,0);
		Arrays.fill(vis, false);
		max_dist=0;
		dfs(max_node,0);
		out.println(max_dist);
		out.close();
	}
	public static void dfs(int node,int dep)
	{
		vis[node]=true;
		if(max_dist<dep) {max_dist=dep;max_node=node;}
		for(int child:adj[node])
		{
			if(!vis[child])dfs(child,dep+1);
		}
	}
	//returns the index of the smallest element in the array that is greater than or equal to
	//the given element.
	public static int lower_bound(int arr[],int key)
	{
		int index=inf,num=0;
		int left=0,right=arr.length-1;
		while(left<=right)
		{
			int mid=left+(right-left)/2;
			if(arr[mid]>=key) {index=mid;num=arr[mid];right=mid-1;}
			else 
				left=mid+1;
		}
		return index==inf ? arr.length:index;
	}
	//returns the index of the smallest element in the array that is less than or equal to
    //the given element.
	public static int upper_bound(int arr[],int key)
	{
		int index=inf,num=0;
		int left=0,right=arr.length-1;
		while(left<=right)
		{
			int mid=left+(right-left)/2;
			if(arr[mid]<=key) {index=mid;num=arr[mid];left=mid+1;}
			else 
				right=mid-1;
		}
		return index==inf ? arr.length:index;
	}
}
class FastScanner 
{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer("");
		public String next() 
		{
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
			
		}
		public String nextLine() throws IOException
		{
		    return br.readLine();
		}
		int[] sort(int arr[])
		{
			ArrayList<Integer> list = new ArrayList<Integer>();
			for(int i:arr)list.add(i);
			Collections.sort(list);
			for(int i=0;i<arr.length;i++)
			{
				arr[i]=list.get(i);
			}
			return arr;
		}
		char[] charsort(char arr[])
	        {
	    	ArrayList<Character> list = new ArrayList<>();
	    	for(char c:arr)list.add(c);
	    	Collections.sort(list);
	    	for(int i=0;i<list.size();i++)
	    	{
	    		arr[i]=list.get(i);
	    	}
	    	return arr;
	        }
		long[] longsort(long arr[])
		{
			ArrayList<Long> list = new ArrayList<Long>();
			for(long i:arr)list.add(i);
			Collections.sort(list);
			for(int i=0;i<arr.length;i++)
			{
				arr[i]=list.get(i);
			}
			return arr;
		}
		public int nextInt() 
		{
			return Integer.parseInt(next());
		}
		public int[] readArray(int n)
		{
			int[] arr=new int[n];
			for (int i=0; i<n; i++) arr[i]=nextInt();
			return arr;
		}	
		public long nextLong()
		{
			return Long.parseLong(next());
		}
		public long[] longreadArray(int n) 
		{
			long[] a=new long[n];
			for (int i=0; i<n; i++) a[i]=nextLong();
			return a;
		}
}
