#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;
}