Construct - ĐT

//Make CSP great again
#include <bits/stdc++.h>
#define TASK "TESTCODE"
using namespace std;
const int N = 1e5;
multiset<int> Adj1[N + 1];
int n, m, Low[N + 1], Num[N + 1], Count(0), Component[N + 1], d[N + 1], ComponentCount(0), res = 0, p, check;
bool Free[N + 1], Visited[N + 1];
stack<int> Stack;
vector<int> Adj[N + 1], tmp;
void read()
{
    cin >> n >> m;
    for (int i = 1; i <= m; ++ i)
    {
        int u, v;
        cin >> u >> v;
        Adj1[u].insert(v);
        Adj1[v].insert(u);
        Adj[u].push_back(v);
        Adj[v].push_back(u);
    }
    fill(Free + 1, Free + n + 1, true);
    fill(Visited + 1, Visited + n + 1, false);
}
void Visit(int u)
{
    ++Count;
    Low[u] = Num[u] = Count;
    Stack.push(u);
    for (int v : Adj1[u])
    {
        if (Free[v])
        {
            if (Num[v] != 0)
            {
                Low[u] = min(Low[u], Num[v]);
            }
            else
            {
                auto it = Adj1[v].find(u);
                Adj1[v].erase(it);
                Visit(v);
                Low[u] = min(Low[u], Low[v]);
            }
        }
    }
    if (Low[u] == Num[u])
    {
        ++ComponentCount;
        int v;
        do
        {
            v = Stack.top();
            Stack.pop();
            Component[v] = ComponentCount;
            Free[v] = false;
        }
        while (v != u);
    }
}
void DFS(int u)
{
    if (d[u] > check)
    {
        check = d[u];
        p = u;
    }
    tmp.push_back(u);
    for (int v : Adj[u])
    {
        if (!Visited[v])
        {
            int add = 0;
            if (Component[v] != Component[u])
            {
                add = 1;
            }
            d[v] = d[u] + add;
            Visited[v] = true;
            DFS(v);
        }
    }
}
void Get(int u)
{
    tmp.clear();
    check = 0;
    p = -1;
    Visited[u] = true;
    DFS(u);
    if (p != -1)
    {
        check = 0;
        for (int i : tmp)
        {
            d[i] = 0;
            Visited[i] = false;
        }
        Visited[p] = true;
        DFS(p);
        res = max(res, check);
    }
}
void solve()
{
    for (int i = 1; i <= n; ++ i)
    {
        if (Num[i] == 0)
        {
            Visit(i);
        }
    }
    for (int i = 1; i <= n; ++ i)
    {
        if (!Visited[i])
        {
            Get(i);
        }
    }
    cout << res;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    //freopen(TASK".INP", "r", stdin);
    //freopen(TASK".OUT", "w", stdout);
    int t = 1;
    bool typetest = false;
    if (typetest)
    {
        cin >> t;
    }
    for (int __ = 1; __ <= t; ++ __)
    {
        read();
        solve();
    }
}