#include<bits/stdc++.h>
#include<atcoder/all>
#define rep(i,b) for(int i=0;i<b;i++)
#define rrep(i,b) for(int i=b-1;i>=0;i--)
#define rep1(i,b) for(int i=1;i<b;i++)
#define repx(i,x,b) for(int i=x;i<b;i++)
#define fore(i,a) for(auto i:a)
#define fore1(i,a) for(auto &i:a)
#define rng(x) (x).begin(), (x).end()
#define rrng(x) (x).rbegin(), (x).rend()
#define sz(x) ((int)(x).size())
#define pb push_back
#define fi first
#define se second

using namespace std;
using namespace atcoder;

using ll = long long;
template<typename T> using mpq = priority_queue<T, vector<T>, greater<T>>;
template<typename T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<typename T> bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
template<typename T> ll sumv(const vector<T>&a){ll res(0);for(auto&&x:a)res+=x;return res;}
bool yn(bool a) { if(a) {cout << "Yes" << endl; return 1;} else {cout << "No" << endl; return 0;}}
#define dame { cout << "No" << endl; return 0;}
#define dame1 { cout << -1 << endl; return 0;}
#define test(x) cout << "test" << x << endl;
#define deb(x,y) cout << x << " " << y << endl;
#define deb3(x,y,z) cout << x << " " << y << " " << z << endl;
#define deb4(x,y,z,x2) cout << x << " " << y << " " << z << " " << x2 << endl;
#define out cout << ans << endl;
#define outv fore(yans , ans) cout << yans << "\n";
#define show(x) cerr<<#x<<" = "<<x<<endl;
#define showv(v) {fore(vy , v) {cout << vy << " ";} cout << endl;}
#define showv2(v) fore(vy , v) cout << vy << "\n";
using pll = pair<ll,ll>;
using pil = pair<int,ll>;
using pli = pair<ll,int>;
using pii = pair<int,int>;
using tp = tuple<int ,int ,int>;
using vi = vector<int>;
using vl = vector<ll>;
using vs = vector<string>;
using vb = vector<bool>;
using vpii = vector<pii>;
using vpli = vector<pli>;
using vpll = vector<pll>;
using vpil = vector<pil>;
using vvi = vector<vector<int>>;
using vvl = vector<vector<ll>>;
using vvs = vector<vector<string>>;
using vvb = vector<vector<bool>>;
using vvpii = vector<vector<pii>>;
using vvpli = vector<vector<pli>>;
using vvpll = vector<vpll>;
using vvpil = vector<vpil>;
using mint = modint998244353;
using vm = vector<mint>;
using vvm = vector<vector<mint>>;
vector<int> dx={1,0,-1,0,1,1,-1,-1},dy={0,1,0,-1,1,-1,1,-1};
ll gcd(ll a, ll b) { return a?gcd(b%a,a):b;}
ll lcm(ll a, ll b) { return a/gcd(a,b)*b;}
const double eps = 1e-10;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;

vvi e;
int n;

vvi v1,v2;
vvi dia;

void dfs(int x,int pre,int cnt){

    int f=-1,s=-1;
    int d=0;

    int cnt_tmp = -1;

    fore(y , e[x]){
        cnt_tmp++;

        if(y == pre) continue;

        dfs(y , x , cnt_tmp);

        if (f <= v1[x][cnt_tmp]){
            chmax(s , f);
            chmax(f , v1[x][cnt_tmp]);
        }else{
            chmax(s , v1[x][cnt_tmp]);
            if (v2[x][cnt_tmp]) chmax(s , v2[x][cnt_tmp]);
        }

        chmax(d , dia[x][cnt_tmp]);        
    }

    if(pre != -1){
        v1[pre][cnt] = f+1;
        v2[pre][cnt] = s+1;
        dia[pre][cnt] = max(d , f+s+2);
    }

    return;
}

vvi sum1,sum1r;
vvi sum2,sum2r;
vvi sumd,sumdr;
vi prei;

void dfs2(int x,int pre,int cnt){

    rep(i , sz(e[x])) if (e[x][i] == pre) prei[x] = i;

    int f=0,s=0,d=0;

    if (pre != -1){
        if (cnt != 0){
            chmax(f , sum1[pre][cnt-1]);
            if (sum2[pre][cnt-1]) chmax(s , sum2[pre][cnt-1]);
            if (sumd[pre][cnt-1]) chmax(d , sumd[pre][cnt-1]);
        }
        if (cnt != sz(v1[pre])-1 ){
            chmax(f , sum1r[pre][cnt+1]);
            if (sum2r[pre][cnt+1]) chmax(s , sum2r[pre][cnt+1]);
            if (sumdr[pre][cnt+1]) chmax(d , sumdr[pre][cnt+1]);
        }

        if (0 < cnt && cnt < sz(v1[pre]) -1){
            chmax(s , min(sum1[pre][cnt-1] , sum1r[pre][cnt+1]));
        }

        // if (x == 1){
        //     show(s);
        //     show(cnt);
        //     show(sum2r[pre][cnt+1]);
        // }

        v1[x][prei[x]] = f;
        v2[x][prei[x]] = s;
        dia[x][prei[x]] = max(d , f+s);
    }

    f = -1;
    s = -1;
    d = 0;

    rep(i,sz(e[x])){
        if (f < v1[x][i]){
            chmax(s , f);
            chmax(f , v1[x][i]);
        }else{
            chmax(s , v1[x][i]);
        }

        // chmax(s , v2[x][i]);
        chmax(d , dia[x][i]);

        sum1[x][i] = f+1;
        sum2[x][i] = s+1;
        sumd[x][i] = d;

        // show(x);
        // show(sum2[x][i]);
        // show(v2[x][i]);
    }

    f = -1;
    s = -1;
    d = 0;

    rrep(i,sz(e[x])){
        if (f < v1[x][i]){
            chmax(s , f);
            chmax(f , v1[x][i]);
        }else{
            chmax(s , v1[x][i]);
        }

        // chmax(s , v2[x][i]);
        chmax(d , dia[x][i]);

        sum1r[x][i] = f+1;
        sum2r[x][i] = s+1;
        sumdr[x][i] = d;
    }

    rep(i,sz(e[x])){
        int y = e[x][i];

        if (y == pre) continue;

        dfs2(y , x , i);
    }

    return;
}

ll ans = LINF;

void dfs_ans(int x,int pre){

    rep(i,sz(e[x])){
        int y = e[x][i];

        if (y == pre) continue;

        ll dx = dia[x][i];
        ll dy = dia[y][prei[y]];

        ll tmp = max({dx , dy , (dx+1)/2+(dy+1)/2 + 1});
        chmin(ans , tmp);

        dfs_ans(y , x);
    }

    return;
}

int main(){
    cin>>n;

    e.resize(n);
    v1.resize(n);
    v2.resize(n);
    dia.resize(n);
    sum1.resize(n);
    sum1r.resize(n);
    sum2.resize(n);
    sum2r.resize(n);
    sumd.resize(n);
    sumdr.resize(n);
    prei.resize(n);

    rep(i,n-1){
        int a,b; cin>>a>>b;

        a--; b--;

        e[a].pb(b);
        e[b].pb(a);
    }

    rep(i,n){
        int k = sz(e[i]);
        v1[i].resize(k);
        v2[i].resize(k);
        dia[i].resize(k);
        sum1[i].resize(k);
        sum2[i].resize(k);
        sumd[i].resize(k);
        sum1r[i].resize(k);
        sum2r[i].resize(k);
        sumdr[i].resize(k);
    }

    dfs(0 , -1 , 0);
    dfs2(0 , -1 , 0);

    dfs_ans(0 , -1);

    // rep(i,n){
    //     int k = sz(e[i]);

    //     rep(j,k) deb3(i,j,sum1[i][j]);
    // }

    out;
    

    return 0;
}