#include<bits/stdc++.h>

using namespace std;

// #pragma GCC target ("avx2")
// #pragma GCC optimization ("O3")
// #pragma GCC optimization ("unroll-loops")

//using namespace chrono;

typedef long long ll;
typedef unsigned long long ull;
typedef vector< int > vi;
typedef vector< ll > V;
typedef map<int, int > mp;

#define pb push_back
#define FastIO ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define F first
#define S second

#define debug cout << -1 << endl;
#define REP(i, a, b) for(int i=a; i<b; i++)
#define f0r(i, n) for (int i = 0; i < n; ++i)
#define f0r1(i, n) for (int i = 1; i <= n; ++i)
#define r0f(i, n) for(int i=n-1; i>=0; i--)
#define r0f1(i, n) for(int i=n; i>=1; i--)
#define fore(a, x) for (auto& a : x)
#define fori(i, a, b) for (int i = (a); i < (b); ++i)

#define MP make_pair
#define UB upper_bound
#define LB lower_bound
#define nw cout << "\n"

#define issq(x) (((ll)(sqrt((x))))*((ll)(sqrt((x))))==(x))
#define rev(v) reverse(v.begin(),v.end())
#define asche cerr<<"Ekhane asche\n";
#define rev(v) reverse(v.begin(),v.end())
#define srt(v) sort(v.begin(),v.end())
#define grtsrt(v) sort(v.begin(),v.end(),greater<ll>())
#define all(v) v.begin(),v.end()
#define mnv(v) *min_element(v.begin(),v.end())
#define mxv(v) *max_element(v.begin(),v.end())
#define valid(tx,ty) (tx>=0 && tx<r && ty>=0 && ty<n)
#define one(x) __builtin_popcount(x)

#define dag cerr << "-----------------------------------------\n";


//#define ordered_set tree<ll, null_type,less_equal<ll>, rb_tree_tag,tree_order_statistics_node_update>

//#define pop pop_back
#define setPrec(x) cout << fixed << setprecision(x)

// typedef tree<int, null_type, less<int>, rb_tree_tag,
// tree_order_statistics_node_update> ordered_set;

// int count(int l, int r, ordered_set &st) {
//     return st.order_of_key(r+1) - st.order_of_key(l);
// }

// #define sz(a) (int)a.sz()
//#define fin cin
//#define fout cout
const int INF = 1e9;
const ll MOD = (ll)1e9+7;
const ll INFL = 1e18;
const ll mnINF = -1e18;
const double diff = 10e-6;
const int maxn = 1000002;
const int MX = 100002;
const double PI = acos(-1);
using namespace std;
#define MAX 10000002


const double bruh = .00000001;

// int dx[] = {-1, 0, 1};
// int dy[] = {-1, 0, 1};

int dx[] = {-1, 0, 0, 1};
int dy[] = {0, -1, 1, 0};
// int dx[] = {0, 1};
// int dy[] = {-1, 0};

const int N = 1002;

map< int, vector< int > > adj;
int deg[100002];
int dist[100002];
int dist2[100002];

int find_dia(vector< int > cc, int s)
{
    int mx = 0;
    queue< int > q;
    q.push(s);
    for(auto x: cc) {
        dist[x] = -1;
    }
    dist[s] = 0;
    while(!q.empty()) {
        int c = q.front();
        q.pop();
        mx = max(mx, dist[c]);
        for(auto x: adj[c]) {
            if(dist[x]==-1) {
                dist[x] = dist[c]+1;
                q.push(x);
            }
        }
    }
    return mx;
}

// int find_dia(int s) {

// }

vector< int > find_cc(int s)
{
    vi ans;
    queue< int > q;
    q.push(s);
    dist[s] = 0;
    int last = 0, mx = 0;
    while(!q.empty()) {
        int c = q.front();
        ans.pb(c);
        q.pop();
        if(mx<dist[c]) {
            last = c;
            mx = dist[c];
        }
        for(auto x: adj[c]) {
            if(dist[x]==-1) {
                dist[x] = dist[c] + 1;
                q.push(x);
            }
        }
    }
    ans.pb(last);
    return ans;
}

void solve()
{
    int n, m;
    cin >> n >> m;
    f0r(i, m) {
        int a, b;
        cin >> a >> b;
        adj[a].pb(b);
        adj[b].pb(a);
        deg[a]++; deg[b]++;
    }
    vi radii(3, 0);
    int max_dia = 0;
    memset(dist, -1, sizeof(dist));
    f0r(i, n) {
        // asche;
        if(dist[i]!=-1) continue;
        vector< int > cc = find_cc(i);
        int dNode = cc.back();
        cc.pop_back();
        int dia = find_dia(cc, dNode);
        max_dia = max(max_dia, dia);
        // cout << dia << " ";
        int rad = (dia+1)/2;
        if(rad>radii[2]) {
            radii[2] = rad;
        }
        srt(radii);
    }
    cout << max({max_dia, radii[0] + radii[1] + 1, radii[1] + radii[2] + 2}) << "\n";
}

void setIO(string name = "") { // name is nonempty for USACO file I/O

    ios_base::sync_with_stdio(0); cin.tie(0); // see Fast Input & Output

    // alternatively, cin.tie(0)->sync_with_stdio(0);

    if (name.size()) {

        freopen((name+".in").c_str(), "r", stdin); // see Input & Output

        freopen((name+".out").c_str(), "w", stdout);
    }
}

int32_t main()
{
//#ifndef ONLINE_JUDGE
//    freopen("inputf.in", "r", stdin);
//    freopen("outputf.in", "w", stdout);
//#endif
    // setIO("gates");
    // freopen("ariprog.in","r",stdin);
    // freopen("ariprog.out","w",stdout);
    FastIO;
    // freopen("lightson.in","r",stdin);
    // freopen("lightson.out","w",stdout);
    int t;
    t = 1;
    // preCalc();
    // memset(dp, -1, szof(dp));
    // cin >> t;
    // cin.ignore();
    for(int i=0; i<t; i++) {
        // if(i) nw;
        // cout << "Case " << i+1 << ": ";
        solve();
    }
    return 0;
}