#include using namespace std; #define _p(...) (void)printf(__VA_ARGS__) #define forr(x,arr) for(auto&& x:arr) #define _overload3(_1,_2,_3,name,...) name #define _rep2(i,n) _rep3(i,0,n) #define _rep3(i,a,b) for(int i=int(a);i=int(a);i--) #define rrep(...) _overload3(__VA_ARGS__,_rrep3,_rrep2,)(__VA_ARGS__) #define all(x) (x).begin(), (x).end() #define bit(n) (1LL<<(n)) #define sz(x) ((int)(x).size()) #define fst first #define snd second using ll=long long; using pii=pair;using pll=pair;using pil=pair;using pli=pair; using vs=vector;using vvs=vector;using vvvs=vector; using vb=vector;using vvb=vector;using vvvb=vector; using vi=vector;using vvi=vector;using vvvi=vector; using vl=vector;using vvl=vector;using vvvl=vector; using vd=vector;using vvd=vector;using vvvd=vector; using vpii=vector;using vvpii=vector;using vvvpii=vector; templateistream&operator>>(istream&is,pair&P){is>>P.fst;is>>P.snd;return is;} templateT read(){T t;cin>>t;return t;} templateostream&operator<<(ostream&o,const pair&p){return o<<'('<ostream&operator<<(ostream&o,const vector&t){o<<"{";rep(i,sz(t))o<void e_r_r(vs::iterator it,T a,Args... args){cerr<substr((*it)[0]==' ',it->length())<<" = "<(); vi U(n), V(n); map P; int m = 0; rep(i, n) { int a = read(); int b = read(); int c = read(); int d = read(); if (P.count({a, b})) { U[i] = P[{a, b}]; } else { U[i] = sz(P); P[{a, b}] = U[i]; } if (P.count({c, d})) { V[i] = P[{c, d}]; } else { V[i] = sz(P); P[{c, d}] = V[i]; } m = max(m, max(U[i], V[i]) + 1); } vvi E(m); rep(i, n) { E[U[i]].push_back(V[i]); E[V[i]].push_back(U[i]); } //out(U, V); //out(E); //out(m); vb used(m); rep(i, m) if (used[i] == 0) { int uc = 0; function dfs = [&](int cur, int pre) { used[cur] = 1; forr(nex, E[cur]) { if (nex != pre) { if (used[nex]) uc++; else dfs(nex, cur); } } }; dfs(i, -1); if (uc >= 2) return false; } return true; } void Main() { cout << (solve() ? "YES" : "NO") << endl; } int main() { cin.tie(nullptr); ios::sync_with_stdio(false); Main(); return 0; }