/* #pragma GCC target("avx2") #pragma GCC optimize("O3") #pragma GCC optimize("unroll-loops") //*/ #include // #include // #include using namespace std; // using namespace atcoder; #define DEBUG(x) cerr << #x << ": " << x << endl; #define DEBUG_VEC(v) \ cerr << #v << ":"; \ for (int iiiiiiii = 0; iiiiiiii < v.size(); iiiiiiii++) \ cerr << " " << v[iiiiiiii]; \ cerr << endl; #define DEBUG_MAT(v) \ cerr << #v << endl; \ for (int iv = 0; iv < v.size(); iv++) { \ for (int jv = 0; jv < v[iv].size(); jv++) { \ cerr << v[iv][jv] << " "; \ } \ cerr << endl; \ } typedef long long ll; // #define int ll #define vi vector #define vl vector #define vii vector> #define vll vector> #define vs vector #define pii pair #define pis pair #define psi pair #define pll pair template pair operator+(const pair &s, const pair &t) { return pair(s.first + t.first, s.second + t.second); } template pair operator-(const pair &s, const pair &t) { return pair(s.first - t.first, s.second - t.second); } template ostream &operator<<(ostream &os, pair p) { os << "(" << p.first << ", " << p.second << ")"; return os; } #define X first #define Y second #define rep(i, n) for (int i = 0; i < (int)(n); i++) #define rep1(i, n) for (int i = 1; i <= (int)(n); i++) #define rrep(i, n) for (int i = (int)(n)-1; i >= 0; i--) #define rrep1(i, n) for (int i = (int)(n); i > 0; i--) #define REP(i, a, b) for (int i = a; i < b; i++) #define in(x, a, b) (a <= x && x < b) #define all(c) c.begin(), c.end() void YES(bool t = true) { cout << (t ? "YES" : "NO") << endl; } void Yes(bool t = true) { cout << (t ? "Yes" : "No") << endl; } void yes(bool t = true) { cout << (t ? "yes" : "no") << endl; } void NO(bool t = true) { cout << (t ? "NO" : "YES") << endl; } void No(bool t = true) { cout << (t ? "No" : "Yes") << endl; } void no(bool t = true) { cout << (t ? "no" : "yes") << endl; } template bool chmax(T &a, const T &b) { if (a < b) { a = b; return 1; } return 0; } template bool chmin(T &a, const T &b) { if (a > b) { a = b; return 1; } return 0; } #define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end()); const ll inf = 1000000001; const ll INF = (ll)1e18 + 1; const long double pi = 3.1415926535897932384626433832795028841971L; int popcount(ll t) { return __builtin_popcountll(t); } // int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1}; // int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 }; vi dx = {0, 1, 0, -1}, dy = {-1, 0, 1, 0}; // vi dx2 = { 1,1,0,-1,-1,-1,0,1 }, dy2 = { 0,1,1,1,0,-1,-1,-1 }; struct Setup_io { Setup_io() { ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0); cout << fixed << setprecision(25); } } setup_io; // const ll MOD = 1000000007; const ll MOD = 998244353; // #define mp make_pair //#define endl '\n' class HLD { private: void dfs_sz(int v) { for (int &u : G[v]) if (u == par[v]) swap(u, G[v].back()); if (~par[v]) G[v].pop_back(); for (int &u : G[v]) { par[u] = v; dep[u] = dep[v] + 1; dfs_sz(u); sub[v] += sub[u]; if (sub[u] > sub[G[v][0]]) swap(u, G[v][0]); } } void dfs_hld(int v, int c, int &pos) { vid[v] = pos++; inv[vid[v]] = v; type[v] = c; for (int u : G[v]) { if (u == par[v]) continue; head[u] = (u == G[v][0] ? head[v] : u); dfs_hld(u, c, pos); } } public: vector> G; vector vid, head, sub, par, dep, inv, type; HLD(int n) : G(n), vid(n, -1), head(n), sub(n, 1), par(n, -1), dep(n, 0), inv(n), type(n) {} void add_edge(int u, int v) { G[u].emplace_back(v); G[v].emplace_back(u); } void build(vector rs = {0}) { int c = 0, pos = 0; for (int r : rs) { dfs_sz(r); head[r] = r; dfs_hld(r, c++, pos); } } int lca(int u, int v) { while (1) { if (vid[u] > vid[v]) swap(u, v); if (head[u] == head[v]) return u; v = par[head[v]]; } } int distance(int u, int v) { return dep[u] + dep[v] - 2 * dep[lca(u, v)]; } // for_each(vertex) // [l, r) <- attention!! template void for_each(int u, int v, const F &f) { while (1) { if (vid[u] > vid[v]) swap(u, v); f(max(vid[head[v]], vid[u]), vid[v] + 1); if (head[u] != head[v]) v = par[head[v]]; else break; } } template T for_each(int u, int v, T ti, const Q &q, const F &f) { T l = ti, r = ti; while (1) { if (vid[u] > vid[v]) { swap(u, v); swap(l, r); } l = f(l, q(max(vid[head[v]], vid[u]), vid[v] + 1)); if (head[u] != head[v]) v = par[head[v]]; else break; } return f(l, r); } // for_each(edge) // [l, r) <- attention!! template void for_each_edge(int u, int v, const F &f) { while (1) { if (vid[u] > vid[v]) swap(u, v); if (head[u] != head[v]) { f(vid[head[v]], vid[v] + 1); v = par[head[v]]; } else { if (u != v) { f(vid[u] + 1, vid[v] + 1); } break; } } } }; template class LazySegmentTree { public: using F = function; // query_func using G = function; // update_func using H = function; // lazy to node (node, lazy, left, right) int n; vector node; vector lazy; T1 e1; T2 e2; F query_func; G update_func; H eval_func; LazySegmentTree(vector a, F query_func, G update_func, H eval_func, T1 e1, T2 e2) : query_func(query_func), update_func(update_func), eval_func(eval_func), e1(e1), e2(e2) { int _n = a.size(); n = 1; while (n < _n) n *= 2; node.resize(2 * n - 1, e1); lazy.resize(2 * n - 1, e2); for (int i = 0; i < _n; i++) node[i + n - 1] = a[i]; for (int i = n - 2; i >= 0; i--) { node[i] = query_func(node[i * 2 + 1], node[i * 2 + 2]); } } // k�Ԗڂ̃m�[�h�ɂ‚��Ēx���]�����s�� inline void eval(int k, int l, int r) { if (lazy[k] != e2) { // Change node[k] = eval_func(node[k], lazy[k], l, r); if (r - l > 1) { lazy[2 * k + 1] = update_func(lazy[2 * k + 1], lazy[k]); lazy[2 * k + 2] = update_func(lazy[2 * k + 2], lazy[k]); } lazy[k] = e2; // Change } } // [a, b)��x�ɂ��� void update(int a, int b, T2 x, int k, int l, int r) { // k �Ԗڂ̃m�[�h�ɑ΂��Ēx���]�����s�� eval(k, l, r); if (b <= l || r <= a) return; if (a <= l && r <= b) { lazy[k] = update_func(lazy[k], x); eval(k, l, r); } else { update(a, b, x, 2 * k + 1, l, (l + r) / 2); update(a, b, x, 2 * k + 2, (l + r) / 2, r); node[k] = query_func(node[2 * k + 1], node[2 * k + 2]); } } void update(int a, int b, T2 x) { update(a, b, x, 0, 0, n); } T1 query(int a, int b, int k, int l, int r) { eval(k, l, r); if (b <= l || r <= a) return e1; if (a <= l && r <= b) return node[k]; T1 resl = query(a, b, 2 * k + 1, l, (l + r) / 2); T1 resr = query(a, b, 2 * k + 2, (l + r) / 2, r); return query_func(resl, resr); } T1 query(int a, int b) { return query(a, b, 0, 0, n); } }; const int N = 200011; vii G(N); void dfs(int now, int par, vi &val) { for (int ch : G[now]) { if (ch == par) continue; dfs(ch, now, val); val[now] += val[ch]; } } signed main() { int n; cin >> n; HLD hld(n); vi u(n - 1), v(n - 1), c(n - 1); rep(i, n - 1) { cin >> u[i] >> v[i] >> c[i]; u[i]--; v[i]--; G[u[i]].push_back(v[i]); G[v[i]].push_back(u[i]); hld.add_edge(u[i], v[i]); } hld.build(); auto f1 = [](ll a, ll b) { return max(a, b); }; auto g = [](ll a, ll b) { return b; }; auto h = [](ll a, ll b, int l, int r) { return b; }; LazySegmentTree seg_ma(vl(n), f1, g, h, -INF, INF); auto f2 = [](ll a, ll b) { return min(a, b); }; LazySegmentTree seg_mi(vl(n), f2, g, h, INF, -INF); rep(i, n - 1) { auto f1 = [&](ll a, ll b) { seg_ma.update(a, b, c[i]); }; hld.for_each_edge(u[i], v[i], f1); auto f2 = [&](ll a, ll b) { seg_mi.update(a, b, c[i]); }; hld.for_each_edge(u[i], v[i], f2); } int ok = inf + 10, ng = -1; vi val(n); while (ng + 1 < ok) { int mid = (ng + ok) / 2; // if (mid < 3) { // DEBUG(mid); // } vi us; rep(i, n - 1) { if (c[i] <= mid) continue; us.push_back(u[i]); us.push_back(v[i]); } if (us.size() == 0) { ok = mid; continue; } fill(all(val), 0); int lc = us[0]; for (int u : us) { val[u] = 1; lc = hld.lca(u, lc); } dfs(0, -1, val); vi leaf; rep(i, n) { if (val[i] == 1) { leaf.push_back(i); } } assert(leaf.size() > 0); if (leaf.size() > 2) { ng = mid; continue; } int lc2 = leaf[0]; for (int u : leaf) { lc2 = hld.lca(u, lc2); } if (leaf.size() == 2 && lc != lc2) { ng = mid; continue; } ll mi = INF, ma = -INF; auto f1 = [&](int a, int b) { mi = min(mi, seg_mi.query(a, b)); }; auto f2 = [&](int a, int b) { ma = max(ma, seg_ma.query(a, b)); }; for (int u : leaf) { hld.for_each_edge(u, lc, f1); hld.for_each_edge(u, lc, f2); } if (ma - mi <= mid) ok = mid; else ng = mid; } cout << ok << endl; }