#include <bits/stdc++.h>
#include "testlib.h"
using namespace std;

struct Edge {
    int u;
    int v;
    Edge(int a, int b) : u(a), v(b) {

    }
};
using Graph = vector<vector<Edge>>;

vector<vector<int>> dp, dp2, dp_;

void dfs(const Graph& G, int v, int p) {
    for (auto nv : G[v]) {
        if (nv.v == p) continue;
        dfs(G, nv.v, v);
    }
    int count_ = -1;
    for (auto c : G[v]) {
        count_++;
        if (c.v == p) continue;
        int count = -1;
        for (auto d : G[c.v]) {
            count++;
            if (d.v == v) continue;
            //cout << v << " " << c.v << " " << d.v << " " << count << " " << count_ << endl;
            if (dp[v][count_] < dp[c.v][count] + 1) {
                dp2[v][count_] = dp[v][count_];
                dp[v][count_] = dp[c.v][count] + 1;
            }
            else if (dp2[v][count_] < dp[c.v][count] + 1) {
                dp2[v][count_] = dp[c.v][count] + 1;
            }
        }
        count = -1;
        dp_[v][count_] = dp[v][count_] + dp2[v][count_];
        for (auto d : G[c.v]) {
            count++;
            if (d.v == v) continue;
            dp_[v][count_] = max(dp_[v][count_], dp_[c.v][count]);
        }
    }
}

void dfs2(const Graph& G, int v, int p) {
    int count_ = -1;
    for (auto c : G[v]) {
        count_++;
        if (c.v == p) {
            int count = -1;
            for (auto d : G[c.v]) {
                count++;
                if (d.v == v) continue;
                if (dp[v][count_] < dp[c.v][count] + 1) {
                    dp2[v][count_] = dp[v][count_];
                    dp[v][count_] = dp[c.v][count] + 1;
                }
                else if (dp2[v][count_] < dp[c.v][count] + 1) {
                    dp2[v][count_] = dp[c.v][count] + 1;
                }
            }
            count = -1;
            dp_[v][count_] = dp[v][count_] + dp2[v][count_];
            for (auto d : G[c.v]) {
                count++;
                if (d.v == v) continue;
                dp_[v][count_] = max(dp_[v][count_], dp_[c.v][count]);
            }
        }
    }
    for (auto nv : G[v]) {
        if (nv.v == p) continue;
        dfs2(G, nv.v, v);
    }
}

int main() {
    registerValidation();
    int N = inf.readInt(2, 100000, "N");
    inf.readEoln();

    Graph G(N);
    vector<int> a(N - 1), b(N - 1), c(N - 1), d(N - 1);
    for (int i = 0; i < N - 1; i++) {
        a[i] = inf.readInt(1, N, "a");
        inf.readSpace();
        b[i] = inf.readInt(1, N, "a");
        inf.readEoln();
        c[i] = G[a[i] - 1].size();
        d[i] = G[b[i] - 1].size();
        G[a[i] - 1].emplace_back(a[i] - 1, b[i] - 1);
        G[b[i] - 1].emplace_back(b[i] - 1, a[i] - 1);
    }
    inf.readEof();

    for (int i = 0; i < N; i++) {
        if (G[i].size() == 0) cout << -1 << endl;
    }

    dp.assign(N, vector<int>(0));
    dp2.assign(N, vector<int>(0));
    dp_.assign(N, vector<int>(0));
    for (int i = 0; i < N; i++) {
        dp[i].assign(G[i].size(), 0);
        dp2[i].assign(G[i].size(), 0);
        dp_[i].assign(G[i].size(), 0);
    }

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

    int ans_ = 1000000;
    for (int i = 0; i < N - 1; i++) {
        ans_ = min(ans_, max(max(dp_[a[i] - 1][c[i]], dp_[b[i] - 1][d[i]]), (dp_[a[i] - 1][c[i]] + 1) / 2 + (dp_[b[i] - 1][d[i]] + 1) / 2 + 1));
    }

    cout << ans_ << endl;
}