#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define rep(x, s, t) for(ll x = (s); (x) <= (t); (x)++) #define per(x, s, t) for(ll x = (s); (x) >= (t); (x)--) #define reps(x, s) for(ll x = 0; (x) < (ll)(s).size(); (x)++) #define chmin(x, y) (x) = min((x), (y)) #define chmax(x, y) (x) = max((x), (y)) #define sz(x) ((ll)(x).size()) #define all(x) (x).begin(),(x).end() #define rall(x) (x).rbegin(),(x).rend() #define outl(...) dump_func(__VA_ARGS__) #define outf(x) cout << fixed << setprecision(16) << (x) << endl #define pb push_back #define fi first #define se second #define inf 2e18 #define eps 1e-9 const double PI = 3.1415926535897932384626433; using namespace std; typedef long long ll; typedef unsigned long long ull; typedef pair P; struct edge{ ll to, cost; edge(){} edge(ll a, ll b){ to = a, cost = b;} }; const int dx[] = {1, 0, -1, 0}, dy[] = {0, -1, 0, 1}; const int mod = 1000000007; //const int mod = 998244353; struct mint{ int x; mint(ll y = 0){if(y < 0 || y >= mod) y = (y%mod+mod)%mod; x = y;} mint(const mint &ope) {x = ope.x;} mint operator-(){return mint(-x);} mint operator+(const mint &ope){return mint(x) += ope;} mint operator-(const mint &ope){return mint(x) -= ope;} mint operator*(const mint &ope){return mint(x) *= ope;} mint operator/(const mint &ope){return mint(x) /= ope;} mint& operator+=(const mint &ope){x += ope.x; if(x >= mod) x -= mod; return *this;} mint& operator-=(const mint &ope){x += mod - ope.x; if(x >= mod) x -= mod; return *this;} mint& operator*=(const mint &ope){ll tmp = x; tmp *= ope.x, tmp %= mod; x = tmp; return *this;} mint& operator/=(const mint &ope){ ll n = mod-2; mint mul = ope; while(n){if(n & 1) *this *= mul; mul *= mul; n >>= 1;} return *this; } mint inverse(){return mint(1) / *this;} bool operator ==(const mint &ope){return x == ope.x;} bool operator !=(const mint &ope){return x != ope.x;} bool operator <(const mint &ope)const{return x < ope.x;} }; mint modpow(mint a, ll n){ if(n == 0) return mint(1); if(n % 2) return a * modpow(a, n-1); else return modpow(a*a, n/2); } istream& operator >>(istream &is, mint &ope){ll t; is >> t, ope = mint(t); return is;} ostream& operator <<(ostream &os, mint &ope){return os << ope.x;} ostream& operator <<(ostream &os, const mint &ope){return os << ope.x;} ll modpow(ll a, ll n, ll mod){ if(n == 0) return 1; if(n % 2) return ((a%mod) * (modpow(a, n-1, mod)%mod)) % mod; else return modpow((a*a)%mod, n/2, mod) % mod; } vector fact, fact_inv; void make_fact(int n){ fact.resize(n+1), fact_inv.resize(n+1); fact[0] = mint(1); rep(i, 1, n) fact[i] = fact[i-1] * mint(i); fact_inv[n] = fact[n].inverse(); per(i, n-1, 0) fact_inv[i] = fact_inv[i+1] * mint(i+1); } mint comb(int n, int k){ if(n < 0 || k < 0 || n < k) return mint(0); return fact[n] * fact_inv[k] * fact_inv[n-k];} mint perm(int n, int k){ return comb(n, k) * fact[k]; } template T comb2(ll n, ll k){ if(n < 0 || k < 0 || n < k) return T(0); T ret = 1; rep(i, 1, k) ret *= n-k+i, ret /= i; return ret;} vector prime, pvec, qrime; void make_prime(int n){ prime.resize(n+1); rep(i, 2, n){ if(prime[i] == 0) pvec.push_back(i), prime[i] = i; for(auto p : pvec){ if(i*p > n || p > prime[i]) break; prime[i*p] = p;} } } void make_qrime(int n){ qrime.resize(n+1); rep(i, 2, n){int ni = i / prime[i]; if(prime[i] == prime[ni]) qrime[i] = qrime[ni] * prime[i]; else qrime[i] = prime[i];} } void factorize(ll n, map &mp){ mp.clear(); for(auto p : pvec) while(n % p == 0) mp[p]++, n /= p; if(n > 1) mp[n]++; } bool exceed(ll x, ll y, ll m){return y > 0 && x >= m / y + 1;} void mark(){ cout << "*" << endl; } void yes(){ cout << "YES" << endl; } void no(){ cout << "NO" << endl; } ll floor(ll a, ll b){ if(b < 0) a *= -1, b *= -1; if(a >= 0) return a/b; else return -((-a+b-1)/b); } ll ceil(ll a, ll b){ if(b < 0) a *= -1, b *= -1; if(a >= 0) return (a+b-1)/b; else return -((-a)/b); } ll modulo(ll a, ll b){ b = abs(b); return a - floor(a, b) * b;} ll sgn(ll x){ if(x > 0) return 1; if(x < 0) return -1; return 0;} ll gcd(ll a, ll b){if(b == 0) return a; return gcd(b, a%b);} ll lcm(ll a, ll b){return a/gcd(a, b)*b;} ll arith(ll x){return x*(x+1)/2;} ll arith(ll l, ll r){return arith(r) - arith(l-1);} ll digitnum(ll x, ll b = 10){ll ret = 0; for(; x; x /= b) ret++; return ret;} ll digitsum(ll x, ll b = 10){ll ret = 0; for(; x; x /= b) ret += x % b; return ret;} string lltos(ll x, ll b = 10){if(x == 0) return "0"; string ret; for(;x;x/=b) ret += x % b + '0'; reverse(all(ret)); return ret;} ll stoll(string &s, ll b = 10){ll ret = 0; for(auto c : s) ret *= b, ret += c - '0'; return ret;} template void uniq(T &vec){sort(all(vec)); vec.erase(unique(all(vec)), vec.end());} int popcount(ull x){ x -= ((x>>1)&0x5555555555555555ULL), x = (x & 0x3333333333333333ULL) + ((x>>2) & 0x3333333333333333ULL); return (((x + (x>>4)) & 0x0F0F0F0F0F0F0F0FULL) * 0x0101010101010101ULL) >> 56; } template pair& operator+=(pair &s, const pair &t){s.first += t.first, s.second += t.second; return s;} template pair& operator-=(pair &s, const pair &t){s.first -= t.first, s.second -= t.second; return s;} 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 T dot(const pair &s, const pair &t){return s.first*t.first + s.second*t.second;} template T cross(const pair &s, const pair &t){return s.first*t.second - s.second*t.first;} template T mdist(pair s, pair t){return abs(s.first-t.first) + abs(s.second-t.second);} template T cdist(pair s, pair t){return max(abs(s.first-t.first), abs(s.second-t.second));} template T edist2(pair s, pair t){return (s.first-t.first)*(s.first-t.first) + (s.second-t.second)*(s.second-t.second);} template ostream& operator << (ostream& os, vector& vec){reps(i, vec) os << vec[i] << " "; return os;} template ostream& operator << (ostream& os, const vector& vec){reps(i, vec) os << vec[i] << " "; return os;} template ostream& operator << (ostream& os, list& ls){for(auto x : ls) os << x << " "; return os;} template ostream& operator << (ostream& os, const list& ls){for(auto x : ls) os << x << " "; return os;} template ostream& operator << (ostream& os, deque& deq){reps(i, deq) os << deq[i] << " "; return os;} template ostream& operator << (ostream& os, pair& ope){ os << "(" << ope.first << ", " << ope.second << ")"; return os;} template ostream& operator << (ostream& os, const pair& ope){ os << "(" << ope.first << ", " << ope.second << ")"; return os;} template ostream& operator << (ostream& os, map& ope){ for(auto p : ope) os << "(" << p.first << ", " << p.second << "),";return os;} template ostream& operator << (ostream& os, set& ope){for(auto x : ope) os << x << " "; return os;} template ostream& operator << (ostream& os, multiset& ope){for(auto x : ope) os << x << " "; return os;} template void outa(T a[], ll s, ll t){rep(i, s, t){ cout << a[i]; if(i < t) cout << " ";} cout << endl;} template ostream& operator << (ostream& os, array& arr){reps(i, arr) os << arr[i] << " "; return os;} template ostream& operator << (ostream& os, const array& arr){reps(i, arr) os << arr[i] << " "; return os;} void dump_func(){cout << endl;} template void dump_func(Head &&head, Tail &&... tail){cout << head; if(sizeof...(Tail) > 0) cout << " "; dump_func(std::move(tail)...);} struct Diameter{ ll n; vector dtmp, diam, depth; Diameter(){} void distdfs(vector G[], int v, int p, ll d) { dtmp[v] = d; for(auto e : G[v]){ ll u = e.to, c = e.cost; if(u == p) continue; distdfs(G, u, v, d+c); } } bool recdfs(vector G[], int v, int p, int t) { if(v == t){ diam.push_back(v); return true; } bool ret = false; for(auto e : G[v]){ ll u = e.to; if(u == p) continue; ret |= recdfs(G, u, v, t); } if(ret) diam.push_back(v); return ret; } //頂点は1-indexedにするべし。直径の長さを返す。直径の頂点列をdiamに格納す。各点を根としたときの深さをdepthに格納する。 ll init(vector G[], int n) { dtmp.resize(n+1); depth.resize(n+1); distdfs(G, 1, -1, 0); ll max_val = -1, max_v; for(int i = 1; i <= n; i++){ if(max_val < dtmp[i]) max_val = dtmp[i], max_v = i; } ll u = max_v; distdfs(G, u, -1, 0); max_val = -1; for(int i = 1; i <= n; i++){ depth[i] = dtmp[i]; if(max_val < dtmp[i]) max_val = dtmp[i], max_v = i; } ll v = max_v; distdfs(G, v, -1, 0); for(int i = 1; i <= n; i++) depth[i] = max(depth[i], dtmp[i]); recdfs(G, u, -1, v); return max_val; } }; ll n; vector G[100005]; P dp[100005], dp2[100005]; void dfs(int v, int p, P dp[]) { ll dep = 0, diam = 0; vector vec; for(auto e : G[v]){ ll u = e.to; if(u == p) continue; dfs(u, v, dp); chmax(dep, dp[u].fi+1); chmax(diam, dp[u].se); vec.pb(dp[u].fi+1); } vec.pb(0), vec.pb(0); sort(rall(vec)); chmax(diam, vec[0]+vec[1]); dp[v] = P(dep, diam); } int main(void) { ios::sync_with_stdio(0); cin.tie(0); cin >> n; ll u, v; rep(i, 1, n-1){ cin >> u >> v; G[u].pb(edge(v, 1)); G[v].pb(edge(u, 1)); } Diameter diam; diam.init(G, n); dfs(diam.diam.front(), -1, dp); dfs(diam.diam.back(), -1, dp2); ll ans = inf; reps(i, diam.diam){ if(i == 0) continue; ll u = diam.diam[i-1], v = diam.diam[i]; chmin(ans, max(max(dp[v].se, dp2[u].se), ceil(dp[v].se,2)+ceil(dp2[u].se,2)+1)); } outl(ans); return 0; }