#include <bits/stdc++.h>

#define close_all { \
out.close();      \
in.close(); }

using namespace std;

#define int long long

int n;
map<int, vector<int>> graph;
set<int> curr;
bool chk;

vector<int> bfs(int start) {
  deque<int> q;
  q.push_back(start);
  map<int, bool> used;
  vector<int> d(n);
  used[start] = true;
  while (!q.empty()) {
    int v = q.front();
    q.pop_front();
    for (int i = 0; i < graph[v].size(); ++i) {
      int to = graph[v][i];
      if (!used[to]) {
        used[to] = true;
        q.push_back(to);
        d[to] = d[v] + 1;
      }
    }
  }
  return d;
}

int diameter() {
  int v, u, w;
  v = u = w = 0;
  vector<int> d = bfs(v);
  for (int i = 0; i < n; ++i) {
    if (d[i] > d[u]) {
      u = i;
    }
  }
  d = bfs(u);
  for (int i = 0; i < n; ++i) {
    if (d[i] > d[w]) {
      w = i;
    }
  }
  return d[w];
}

signed main() {
  int m;
  cin >> n >> m;

  for (int i = 0; i < m; ++i) {
    int a, b;
    cin >> a >> b;
    graph[a - 1].push_back(b - 1);
    graph[b - 1].push_back(a - 1);
  }

  cout << diameter();
  return 0;
}