#include <bits/stdc++.h>

using ll = long long;
using namespace std;

const int MAXN = 1001;

vector<int> g[MAXN];
int d[MAXN], ans = 0;

void dfs(int u, int p = -1, int depth = 1) {
    d[u] = depth;
    for (int v : g[u]) {
        if (v != p) {
            if (d[v]) ans = max(ans, abs(d[v]-d[u]+1));
            else dfs(v, u, depth + 1);
        }
    }
}

void solve() {
    int n, m; cin >> n >> m;
    for (int i = 0; i < m; i++) {
        int u, v; cin >> u >> v;
        g[u].emplace_back(v);
        g[v].emplace_back(u);
    }
    dfs(1);
    cout << ans << "\n";
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}