#include <bits/stdc++.h>
#pragma region Utility
#define speed cin.tie(0); ios::sync_with_stdio(0)
#define cinv(v) for (auto& e : v) cin >> e;
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define size(v) (int)v.size()
#define has(s, e) s.count(e)
#define max_index(v) max_element(all(v)) - v.begin()
#define min_index(v) min_element(all(v)) - v.begin()
#define smax(x, y) x = max(x, y)
#define smin(x, y) x = min(x, y)
#define sum(v) accumulate(all(v), 0)
#define product(v, T) accumulate(all(v), 1, multiplies<T>())
using namespace std;
using ll = long long;
using point = array<int, 2>;
int max(point p) { return max(p[0], p[1]); }
int min(point p) { return min(p[0], p[1]); }
template <typename T>
vector<T> prefix_sum(const vector<T>& v) {
vector<T> result(size(v));
partial_sum(all(v), result.begin());
return result;
}
#pragma endregion
int N, M;
vector<int> vis;
vector<vector<int>> g;
int result;
void dfs(int u, int t) {
if (vis[u]) {
smax(result, t - vis[u]);
return;
}
vis[u] = t;
for (int neigh : g[u]) {
dfs(neigh, t + 1);
}
}
int main() {
speed;
cin >> N >> M;
g.resize(N + 1);
vis.resize(N + 1);
while (M--) {
int u, v;
cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
dfs(1, 0);
cout << result;
}