#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 1;
vector <int> adj[maxn];
bool vis[maxn];
int node = 0, max_dis = -1;
void dfs(int s, int p, int d) {
if (d > max_dis) {
node = s;
max_dis = d;
}
vis[s] = true;
for (auto i : adj[s]) {
if (i == p)
continue;
dfs(i, s, d+1);
}
}
int main() {
int n, m;
cin >> n >> m;
for (int i = 0; i < m; i++) {
int a, b;
cin >> a >> b;
adj[a].push_back(b);
adj[b].push_back(a);
}
vector <pair <int, int>> endpoints;
for (int i = 1; i <= n; i++) {
if (vis[i])
continue;
max_dis = -1;
endpoints.emplace_back();
dfs(i, i, 0);
endpoints.back().first = node;
max_dis = -1;
dfs(node, node, 0);
endpoints.back().second = node;
}
for (int i = 0; i + 1 < (int)endpoints.size(); i++) {
int a = endpoints[i].second, b = endpoints[i+1].first;
adj[a].push_back(b);
adj[b].push_back(a);
}
max_dis = -1;
dfs(endpoints.back().second, 0, 0);
cout << max_dis+1 << '\n';
}
