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 sun.reflect.generics.tree.Tree;

import javax.swing.event.TreeSelectionEvent;
import javax.swing.plaf.synth.SynthTextAreaUI;
import java.io.*;
import java.net.Inet4Address;
import java.text.DecimalFormat;
import java.util.*;
import java.awt.Point;

public class Newbie {

    static InputReader sc = new InputReader(System.in);
    static PrintWriter out = new PrintWriter(System.out);

    public static void main(String[] args) throws IOException {
        solver s = new solver();
        int t = 1;
        while (t > 0) {
            s.sol();
            t--;
        }
        out.close();
    }
           /* static class descend implements Comparator<pair1> {
                public int compare(pair1 o1, pair1 o2) {
                    if (o1.pop != o2.pop)
                        return (int) (o1.pop - o2.pop);
                    else
                        return o1.in - o2.in;
                }
            }*/

    static class InputReader {
        public BufferedReader br;
        public StringTokenizer token;

        public InputReader(InputStream stream) {
            br = new BufferedReader(new InputStreamReader(stream), 32768);
            token = null;
        }

        public String sn() {
            while (token == null || !token.hasMoreTokens()) {
                try {
                    token = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return token.nextToken();
        }

        public int ni() {
            return Integer.parseInt(sn());
        }

        public String snl() throws IOException {
            return br.readLine();
        }

        public long nlo() {
            return Long.parseLong(sn());
        }

        public double nd() {
            return Double.parseDouble(sn());
        }

        public int[] na(int n) {
            int a[] = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = sc.ni();
            return a;
        }

        public long[] nal(int n) {
            long a[] = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = sc.nlo();
            return a;
        }
    }

    static class ascend implements Comparator<pair> {
        public int compare(pair o1, pair o2) {
            return o2.b - o1.b;
        }
    }

    static class extra {

        static boolean v[] = new boolean[100001];
        static List<Integer> l = new ArrayList<>();
        static int t;

        static void shuffle(int a[]) {
            for (int i = 0; i < a.length; i++) {
                int t = (int) Math.random() * a.length;
                int x = a[t];
                a[t] = a[i];
                a[i] = x;
            }
        }

        static void shufflel(long a[]) {
            for (int i = 0; i < a.length; i++) {
                int t = (int) Math.random() * a.length;
                long x = a[t];
                a[t] = a[i];
                a[i] = x;
            }
        }

        static int gcd(int a, int b) {
            if (b == 0)
                return a;
            else
                return gcd(b, a % b);
        }

        static boolean valid(int i, int j, int r, int c) {
            if (i >= 0 && i < r && j >= 0 && j < c) {
                // System.out.println(i+" /// "+j);
                return true;
            } else {
                //  System.out.println(i+" //f "+j);
                return false;
            }
        }

        static void seive() {
            for (int i = 2; i < 101; i++) {
                if (!v[i]) {
                    t++;
                    l.add(i);
                    for (int j = 2 * i; j < 101; j += i)
                        v[j] = true;
                }
            }
        }

        static int binary(LinkedList<Integer> a, long val, int n) {
            int mid = 0, l = 0, r = n - 1, ans = 0;
            while (l <= r) {
                mid = (l + r) >> 1;
                if (a.get(mid) == val) {
                    r = mid - 1;
                    ans = mid;
                } else if (a.get(mid) > val)
                    r = mid - 1;
                else {
                    l = mid + 1;
                    ans = l;
                }
            }
            return (ans + 1);
        }

        static long fastexpo(long x, long y) {
            long res = 1;
            while (y > 0) {
                if ((y & 1) == 1) {
                    res *= x;
                }
                y = y >> 1;
                x = x * x;
            }
            return res;
        }

        static long lfastexpo(long x, long y, long p) {
            long res = 1;
            x = x % p;
            while (y > 0) {
                if ((y & 1) == 1) {
                    res = (res * x) % p;
                }
                y = y >> 1;
                x = (x * x) % p;
            }
            return res;
        }

               /* void dijsktra(int s, List<pair> l[], int n) {
                    PriorityQueue<pair> pq = new PriorityQueue<>(new ascend());
                    int dist[] = new int[100005];
                    boolean v[] = new boolean[100005];
                    for (int i = 1; i <= n; i++)
                        dist[i] = 1000000000;
                    dist[s] = 0;
                    for (int i = 1; i < n; i++) {
                        if (i == s)
                            pq.add(new pair(s, 0));
                        else
                            pq.add(new pair(i, 1000000000));
                    }
                    while (!pq.isEmpty()) {
                        pair node = pq.remove();
                        v[node.a] = true;
                        for (int i = 0; i < l[node.a].size(); i++) {
                            int v1 = l[node.a].get(i).a;
                            int w = l[node.a].get(i).b;
                            if (v[v1])
                                continue;
                            if ((dist[node.a] + w) < dist[v1]) {
                                dist[v1] = dist[node.a] + w;
                                pq.add(new pair(v1, dist[v1]));
                            }
                        }
                    }
                }*/
    }

    static class pair {
        int a;
        int b;

        public pair(int a, int b) {
            this.a = a;
            this.b = b;
        }
    }

    static class pair1 {
        pair p;
        int in;

        public pair1(pair a, int n) {
            this.p = a;
            this.in = n;
        }
    }

    static int inf = 5000013;

    static class solver {
        DecimalFormat df = new DecimalFormat("0.00000000");
        extra e = new extra();
        long mod = (long) (1000000007);
        List<Integer> list[] = new ArrayList[200005];

        void sol() throws IOException {
            int n = sc.ni();
            int m = sc.ni();
            for (int i = 0; i < n; i++)
                list[i] = new ArrayList<>();
            for (int i = 0; i < m; i++) {
                int u = sc.ni() - 1;
                int v = sc.ni() - 1;
                list[u].add(v);
                list[v].add(u);
            }
            max = -1;
            mx = -1;
            dfs(0, 0);
            v = new boolean[n];
            max = -1;
            dfs(mx, 0);
            out.println(max);
        }

        int max, mx;
        boolean v[] = new boolean[200005];

        void dfs(int s, int l) {
            v[s] = true;
            if (l > max) {
                max = l;
                mx = s;
            }
            for (int ver : list[s]) {
                if (!v[ver]) {
                    dfs(ver, l + 1);
                }
            }
        }
    }
}
