#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <ciso646>
#include <cmath>
#include <complex>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;
typedef long long ll;
const ll mod = 1000000007;
const ll INF = (ll)1000000007 * 1000000007;
typedef pair<int, int> P;
#define rep(i, n) for (int i = 0; i < n; i++)
#define per(i, n) for (int i = n - 1; i >= 0; i--)
#define Rep(i, sta, n) for (int i = sta; i < n; i++)
#define Per(i, sta, n) for (int i = n - 1; i >= sta; i--)
typedef long double ld;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ll, ll> LP;
int dx[8] = {1, -1, 0, 0, 1, 1, -1, -1};
int dy[8] = {0, 0, 1, -1, 1, -1, 1, -1};
template <class T>
using max_heap = priority_queue<T>;
template <class T>
using min_heap = priority_queue<T, vector<T>, greater<>>;

template <class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}

template <class T>
bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}

struct edge {
  int to, id, t;
  edge() {}
  edge(int to, int id, int t) : to(to), id(id), t(t) {}
};

int n;
vector<edge> G[200010];
int depth[200010], di[200010][2];
P max_depth[200010][3];

void dfs1(int s, int par, edge pre_e) {
  if (par != -1) depth[s] = depth[par] + 1;
  for (edge e : G[s]) {
    if (e.to == par) continue;
    dfs1(e.to, s, e);
    if (max_depth[s][0].first < max_depth[e.to][2].first + 1) {
      max_depth[s][0] = {max_depth[e.to][2].first + 1, e.id};
      sort(max_depth[s], max_depth[s] + 3);
    }
    if (pre_e.id != -1) chmax(di[pre_e.id][pre_e.t], di[e.id][e.t]);
  }
  if (pre_e.id != -1)
    chmax(di[pre_e.id][pre_e.t], max_depth[s][2].first + max_depth[s][1].first);
}

void dfs2(int s, int par, edge pre_e, int depth_par) {
  set<P> v = {
      max_depth[s][0], max_depth[s][1], max_depth[s][2], {depth_par, pre_e.id}};
  for (edge e : G[s]) {
    if (e.to == par) continue;
    P erased = P(-1, -1);
    // for (P p : v)
    //   if (p.second == e.id) {
    //     erased = p;
    //     v.erase(p);
    //   }
    auto it = v.end();
    it--;
    int d_first = (*it).first;
    it--;
    int d_second = (*it).first;
    dfs2(e.to, s, e, d_first + 1);
    chmax(di[e.id][1 - e.t], d_first + d_second);

    if (erased != P(-1, -1)) v.insert(erased);
  }
}

void dfs3(int s, int par, edge pre_e) {
  for (edge e : G[s]) {
    if (e.to == par) continue;
    if (par != -1) chmax(di[e.id][1 - e.t], di[pre_e.id][1 - pre_e.t]);
    dfs3(e.to, s, e);
  }
}

void solve() {
  cin >> n;
  rep(i, n - 1) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    G[a].push_back({b, i, 0});
    G[b].push_back({a, i, 1});
  }
  rep(i, n) rep(j, 3) max_depth[i][j] = P(0, -1);
  rep(i, n - 1) rep(j, 2) di[i][j] = -1;
  dfs1(0, -1, {0, -1, -1});
  // rep(i, n) cout << depth[i] << " ";
  // cout << "" << endl;
  // rep(i, n) {
  //   rep(j, 3) cout << max_depth[i][j].first << " ";
  //   cout << "" << endl;
  // }

  dfs2(0, -1, {0, -1, -1}, 0);
  dfs3(0, -1, {0, -1, -1});
  // rep(i, n - 1) { cout << di[i][0] << " " << di[i][1] << endl; }
  int ans = mod;
  rep(i, n - 1) { chmin(ans, 1 + (di[i][0] + 1) / 2 + (di[i][1] + 1) / 2); }
  cout << ans << endl;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(50);
  solve();
}