#include using namespace std; using uint = unsigned int; using ll = long long; using ull = unsigned long long; using pii = pair; using pll = pair; template using vec = vector; template using vvec = vector>; #define rep(i, n) for (int i = 0; i < (n); i++) #define rrep(i, n) for (int i = int(n) - 1; i >= 0; i--) #define all(x) begin(x), end(x) constexpr char ln = '\n'; template inline int SZ(const Container& v) { return int(v.size()); } template inline void UNIQUE(vector& v) { v.erase(unique(v.begin(), v.end()), v.end()); } template inline bool chmax(T1& a, T2 b) { if (a < b) { a = b; return true; } return false; } template inline bool chmin(T1& a, T2 b) { if (a > b) { a = b; return true; } return false; } inline int topbit(ull x) { return x == 0 ? -1 : 63 - __builtin_clzll(x); } inline int botbit(ull x) { return x == 0 ? 64 : __builtin_ctzll(x); } inline int popcount(ull x) { return __builtin_popcountll(x); } inline int kthbit(ull x, int k) { return (x >> k) & 1; } inline constexpr long long TEN(int x) { return x == 0 ? 1 : TEN(x - 1) * 10; } const string YESNO[2] = {"NO", "YES"}; const string YesNo[2] = {"No", "Yes"}; inline void YES(bool t = true) { cout << YESNO[t] << "\n"; } inline void Yes(bool t = true) { cout << YesNo[t] << "\n"; } template inline void drop(T x) { cout << x << "\n"; exit(0); } inline void print() { cout << "\n"; } template inline void print(const vector& v) { for (auto it = v.begin(); it != v.end(); ++it) { if (it != v.begin()) { cout << " "; } cout << *it; } print(); } template inline void print(const T& x, const Args& ... args) { cout << x << " "; print(args...); } #ifdef MINATO_LOCAL template ostream& operator<<(ostream& os, pair p) { return os << "(" << p.first << ", " << p.second << ")"; } template void debug_tuple(ostream& os, TUPLE _) { (void)os; (void)_; } template void debug_tuple(ostream &os, TUPLE t) { os << (N == 0 ? "" : ", ") << get(t); debug_tuple(os, t); } template ostream& operator<<(ostream& os, tuple t) { os << "("; debug_tuple<0, tuple, Args...>(os, t); return os << ")"; } string debug_delim(int& i) { return i++ == 0 ? "" : ", "; } #define debug_embrace(x) { int i = 0; os << "{"; { x } return os << "}"; } template ostream& operator<<(ostream& os, vector v) { debug_embrace( for (T e : v) { os << debug_delim(i) << e; } ) } template ostream& operator<<(ostream& os, array a) { debug_embrace( for (T e : a) { os << debug_delim(i) << e; } ) } template enable_if_t>, ostream>& operator<<(ostream& os, T(&a)[N]) { debug_embrace( for (T e : a) { os << debug_delim(i) << e; } ) } template ostream& operator<<(ostream& os, set s) { debug_embrace( for (Key e : s) { os << debug_delim(i) << e; }) } template ostream& operator<<(ostream& os, map mp) { debug_embrace( for (auto e : mp) { os << debug_delim(i) << e; }) } template ostream& operator<<(ostream& os, multiset s) { debug_embrace( for (Key e : s) { os << debug_delim(i) << e; }) } template ostream& operator<<(ostream& os, queue q) { debug_embrace( for (; !q.empty(); q.pop()) { os << debug_delim(i) << q.front(); } ) } template ostream& operator<<(ostream& os, deque q) { debug_embrace( for (T e : q) { os << debug_delim(i) << e; } ) } template ostream& operator<<(ostream& os, priority_queue q) { debug_embrace( for (; !q.empty(); q.pop()) { os << debug_delim(i) << q.top(); } ) } template ostream& operator<<(ostream& os, priority_queue, greater> q) { debug_embrace( for (; !q.empty(); q.pop()) { os << debug_delim(i) << q.top(); } ) } void debug_out() { cerr << endl; } template void debug_out(const T& x, const Args& ... args) { cerr << " " << x; debug_out(args...); } #define debug(...) cerr << __LINE__ << " : [" << #__VA_ARGS__ << "] =", debug_out(__VA_ARGS__) #else #define debug(...) (void(0)) #endif struct fast_ios { fast_ios() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); cerr << fixed << setprecision(7); }; } fast_ios_; /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// vector bfs(const vector>& G, int s = 0) { vector ret(G.size(), -1); ret[s] = 0; queue que; que.emplace(s); while (!que.empty()) { int v = que.front(); que.pop(); for (int nv : G[v]) { if (~ret[nv]) continue; ret[nv] = ret[v] + 1; que.emplace(nv); } } return ret; } int main() { int N; cin >> N; vec deg(N); vvec G(N); rep(i,N-1) { int a,b; cin >> a >> b; a--; b--; G[a].emplace_back(b); G[b].emplace_back(a); deg[a]++; deg[b]++; } vec ls; rep(i,N) { if (deg[i]==1) ls.emplace_back(i); } auto dist = bfs(G,ls[0]); int D = *max_element(all(dist)); if (D&1) { Yes(SZ(ls)==2); return 0; } int m; rep(i,N) { if (D/2==dist[i]) { m = i; break; } } auto dist2 = bfs(G,m); rep(i,N) { if (i==m) continue; if (deg[i]==1) { if (dist2[i]!=D/2) drop("No"); } else { if (deg[i]!=2) drop("No"); } } Yes(1); }