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.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.BufferedWriter;
import java.util.InputMismatchException;
import java.io.IOException;
import java.util.ArrayList;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.io.InputStream;
/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Alex
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        OutputWriter out = new OutputWriter(outputStream);
        TaskC2 solver = new TaskC2();
        solver.solve(1, in, out);
        out.close();
    }
    static class TaskC2 {
        ArrayList<Integer>[] adj;
        int res = 0;
        IntIntPair dfs(int cur, int prev) {
            int dist = 0, num = cur;
            for (int nxt : adj[cur]) {
                if (nxt != prev) {
                    IntIntPair get = dfs(nxt, cur);
                    if (get.first + 1 > dist) {
                        dist = get.first + 1;
                        num = get.second;
                    }
                }
            }
            res = Math.max(res, dist);
            return new IntIntPair(dist, num);
        }
        public void solve(int testNumber, InputReader in, OutputWriter out) {
            int n = in.readInt(), m = in.readInt();
            ArrayList<Integer>[] adj = new ArrayList[n];
            for (int i = 0; i < adj.length; i++)
                adj[i] = new ArrayList<>();
            for (int i = 0; i < m; i++) {
                int a = in.readInt() - 1, b = in.readInt() - 1;
                adj[a].add(b);
                adj[b].add(a);
            }
            this.adj = adj;
            int cur = 0;
            for (int i = 0; i < 3; i++) {
                cur = dfs(cur, -1).second;
            }
            out.printLine(res);
        }
    }
    static 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 close() {
            writer.close();
        }
        public void printLine(int i) {
            writer.println(i);
        }
    }
    static class IntIntPair implements Comparable<IntIntPair> {
        public final int first;
        public final int second;
        public IntIntPair(int first, int second) {
            this.first = first;
            this.second = second;
        }
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            IntIntPair pair = (IntIntPair) o;
            return first == pair.first && second == pair.second;
        }
        public int hashCode() {
            int result = Integer.hashCode(first);
            result = 31 * result + Integer.hashCode(second);
            return result;
        }
        public String toString() {
            return "(" + first + "," + second + ")";
        }
        @SuppressWarnings ({"unchecked"})
        public int compareTo(IntIntPair o) {
            int value = Integer.compare(first, o.first);
            if (value != 0) {
                return value;
            }
            return Integer.compare(second, o.second);
        }
    }
    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private InputReader.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 readInt() {
            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 boolean isSpaceChar(int c) {
            if (filter != null)
                return filter.isSpaceChar(c);
            return isWhitespace(c);
        }
        public static boolean isWhitespace(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }
}

