#include <bits/stdc++.h>
using namespace std;

#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define FOR(i, a, b) for (int i = (a); i<(b); ++i)
#define RFOR(i, b, a) for (int i = (b)-1; i>=(a); --i)
#define MP make_pair
#define PB push_back
#define F first
#define S second

typedef long long LL;
typedef pair<int, int> PII;
typedef vector<int> VI;

const int N = 1 << 17;

vector<int> g[N];
bool used[N];
int maxD, maxV;

void dfs(int v, int p, int d) {
	used[v] = true;
	if (d > maxD) {
		maxD = d;
		maxV = v;
	}
	for (int to : g[v]) {
		if (to != p) {
			dfs(to, v, d + 1);
		}
	}
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n, m;
	cin >> n >> m;
	while (m--) {
		int u, v;
		cin >> u >> v;
		g[u].push_back(v);
		g[v].push_back(u);
	}
	vector<int> w;
	FOR(i, 0, n) {
		if (used[i]) {
			continue;
		}
		maxD = -1;
		dfs(i, -1, 0);
		maxD = -1;
		dfs(maxV, -1, 0);
		w.push_back((maxD + 1) / 2);
	}
	sort(ALL(w));
	int ans = w.back();
	if (SZ(w) >= 2) {
		ans = max(ans, w.back() + 1 + w[SZ(w) - 2]);
	}
	if (SZ(w) >= 3) {
		ans = max(ans, w[SZ(w) - 2] + 2 + w[SZ(w) - 3]);
	}
	cout << ans << "\n";
	return 0;
}