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
import java.util.*;
import java.io.*;
import java.math.*;
public class Main7
{
	static int mod=1000000007;
	static class Pair
    {
        int x;
        int y;
		int z;
		Pair(int x, int y,int z)
        {
            this.x=x;
            this.y=y;
			this.z=z;
        }
    }
    public static long pow(long a, long b,long m)
    {
        long result=1;
        while(b>0)
        {
            if (b % 2 != 0)
            {
                result=(result*a)%m;
                b--;
            } 
            a=(a%mod*a%m)%m;
            b /= 2;
        }   
        return result;
    }
	public static long pow1(long a, long b)
    {
        long result=1;
        while(b>0)
        {
            if (b % 2 != 0)
            {
                result=(result*a);
                b--;
            } 
            a=(a%mod*a);
            b /= 2;
        }   
        return result;
    }
	public static int[] sort(int[] a)
    {
        int n=a.length;
        ArrayList<Integer> ar=new ArrayList<>();
        for(int i=0;i<a.length;i++)
        {
            ar.add(a[i]);
        }
        Collections.sort(ar);
        for(int i=0;i<n;i++)
        {
            a[i]=ar.get(i);
        }
        return a;
    }
	static ArrayList<ArrayList<Integer>> graph;
	static public void main(String args[])throws IOException
	{
		int tt=1;
		StringBuilder sb=new StringBuilder();
		for(int ttt=1;ttt<=tt;ttt++)
		{
			int n=i();
			int m=i();
			int[] a=new int[m];
			int[] b=new int[m];
			graph=new ArrayList<>();
			for(int i=0;i<n;i++)
				graph.add(new ArrayList<>());
			for(int i=0;i<m;i++)
			{
				a[i]=i()-1;
				b[i]=i()-1;
				graph.get(a[i]).add(b[i]);
				graph.get(b[i]).add(a[i]);
			}
			node=0;
			max=0;
			max1=0;
			boolean[] visited=new boolean[n];
			dfs(0,visited,0);
			visited=new boolean[n];
			recur(node,visited,0);
			pln(max+"");
		}
		System.out.print(sb.toString());
	}
	static int max1=0,max=0,node=0;
	static void dfs(int src, boolean[] visited,int count)
	{
		visited[src]=true;
		if(max1<count)
		{
			max1=count;
			node=src;
		}
		ArrayList<Integer> ar=graph.get(src);
		for(int i=0;i<ar.size();i++)
		{
			if(visited[ar.get(i)]==false)
			{
				dfs(ar.get(i),visited,count+1);
			}
		}
	}
	static void recur(int src, boolean[] visited,int count)
	{
		visited[src]=true;
		if(max<count)
			max=count;
		ArrayList<Integer> ar=graph.get(src);
		for(int i=0;i<ar.size();i++)
		{
			if(visited[ar.get(i)]==false)
			{
				recur(ar.get(i),visited,count+1);
			}
		}
	}
			/**/
	static InputReader in=new InputReader(System.in);
	static OutputWriter out=new OutputWriter(System.out);
	public static long l()
	{
		String s=in.String();
		return Long.parseLong(s);
	}
	public static void pln(String value)
	{
		System.out.println(value);
	}
	public static int i()
	{
		return in.Int();
	}
	public static String s()
	{
		return in.String();
	}
}
	class InputReader 
	{
		private InputStream stream;
		private byte[] buf = new byte[1024];
		private int curChar;
		private int numChars;
		private SpaceCharFilter filter;
	 
		public InputReader(InputStream stream) {
			this.stream = stream;
		}
	 
		public int read() {
			if (numChars== -1)
				throw new InputMismatchException();
			if (curChar >= numChars) {
				curChar = 0;
				try {
					numChars = stream.read(buf);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (numChars <= 0)
					return -1;
			}
			return buf[curChar++];
		}
	 
		public int Int() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			int res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c - '0';
				c = read();
			} while (!isSpaceChar(c));
			return res * sgn;
		}
	 
		public String String() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isSpaceChar(c));
			return res.toString();
		}
	 
		public boolean isSpaceChar(int c) {
			if (filter != null)
				return filter.isSpaceChar(c);
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}
	 
		public String next() {
			return String();
		}
	 
		public interface SpaceCharFilter {
			public boolean isSpaceChar(int ch);
		}
	}
	 
	class OutputWriter {
		private final PrintWriter writer;
	 
		public OutputWriter(OutputStream outputStream) {
			writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
		}
	 
		public OutputWriter(Writer writer) {
			this.writer = new PrintWriter(writer);
		}
	 
		public void print(Object...objects) {
			for (int i = 0; i < objects.length; i++) {
				if (i != 0)
					writer.print(' ');
				writer.print(objects[i]);
			}
		}
	 
		public void printLine(Object...objects) {
			print(objects);
			writer.println();
		}
	 
		public void close() {
			writer.close();
		}
	 
		public void flush() {
			writer.flush();
		}
	 
		}
	 
		class IOUtils {
	 
		public static int[] readIntArray(InputReader in, int size) {
			int[] array = new int[size];
			for (int i = 0; i < size; i++)
				array[i] = in.Int();
			return array;
		}
	 
	} 