#include <bits/stdc++.h>
#include <random>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> p32;
typedef pair<ll, ll> p64;
typedef pair<double, double> pdd;
typedef vector<ll> v64;
typedef vector<int> v32;
typedef vector<vector<int>> vv32;
typedef vector<vector<ll>> vv64;
typedef vector<vector<p64>> vvp64;
typedef vector<p64> vp64;
typedef vector<p32> vp32;
ll MOD = 998244353;
double eps = 1e-12;
#define forn(i, e) for (ll i = 0; i < e; i++)
#define forsn(i, s, e) for (ll i = s; i < e; i++)
#define rforn(i, s) for (ll i = s; i >= 0; i--)
#define rforsn(i, s, e) for (ll i = s; i >= e; i--)
#define ln "\n"
#define dbg(x) cout << #x << " = " << x << ln
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define INF 2e18
#define fast_cin()                    \
    ios_base::sync_with_stdio(false); \
    cin.tie(NULL);                    \
    cout.tie(NULL)
#define all(x) (x).begin(), (x).end()
#define sz(x) ((ll)(x).size())

int main()
{
    fast_cin();
    //ifstream cin("in.txt");

    int n;
    cin >> n;

    int m;
    cin >> m;

    vector<vector<int>> vList(n + 1);

    for (int i = 1; i <= m; i++)
    {
        int v1, v2;
        cin >> v1 >> v2;
        vList[v1].push_back(v2);
        vList[v2].push_back(v1);
    }

    int ans = 0;
    vector<bool> in(n + 1);
    vector<int> stackInd(n + 1);
    stack<int> s;

    s.push(1);
    in[1] = 1;
    stackInd[1] = 1;

    while (!s.empty())
    {
        int v = s.top();
        s.pop();
        in[v] = 1;

        //cout << v << ": " << '\n';

        for (int nextV : vList[v])
        {
            //cout << nextV << " ";
            if (!in[nextV])
            {
                s.push(nextV);
                stackInd[nextV] = stackInd[v] + 1;
            }
            else
            {
                if (in[v])
                {
                    ans = max(ans, stackInd[v] - stackInd[nextV] + 1);
                }
            }
        }
        //cout << '\n';
    }

    cout << ans;

    return 0;
}