#define _CRT_SECURE_NO_WARNINGS #include "bits/stdc++.h" #include //#include "util.k" using namespace std; //呪文 #define DUMPOUT cout #define dump(...) DUMPOUT<<" ";DUMPOUT<<#__VA_ARGS__<<" :["<<__LINE__<<":"<<__FUNCTION__<<"]"< pii; typedef pair pll; typedef pair pdd; typedef pair pss; template ostream& operator << (ostream& ostr, const pair<_KTy, _Ty>& m) { ostr << "{" << m.first << ", " << m.second << "}"; return ostr; } template ostream& operator << (ostream& ostr, const map<_KTy, _Ty>& m) { if (m.empty()) { ostr << "{ }"; return ostr; } ostr << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { ostr << ", " << *itr; } ostr << "}"; return ostr; } template ostream& operator << (ostream& ostr, const vector<_Ty>& v) { if (v.empty()) { ostr << "{ }"; return ostr; } ostr << "{" << v.front(); for (auto itr = ++v.begin(); itr != v.end(); itr++) { ostr << ", " << *itr; } ostr << "}"; return ostr; } template ostream& operator << (ostream& ostr, const set<_Ty>& s) { if (s.empty()) { ostr << "{ }"; return ostr; } ostr << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { ostr << ", " << *itr; } ostr << "}"; return ostr; } template ostream& operator << (ostream& ostr, const stack<_Ty>& s) { if (s.empty()) { ostr << "{ }"; return ostr; } stack<_Ty> t(s); ostr << "{" << t.top(); t.pop(); while (!t.empty()) { ostr << ", " << t.top(); t.pop(); } ostr << "}"; return ostr; } template ostream& operator << (ostream& ostr, const list<_Ty>& l) { if (l.empty()) { ostr << "{ }"; return ostr; } ostr << "{" << l.front(); for (auto itr = ++l.begin(); itr != l.end(); ++itr) { ostr << ", " << *itr; } ostr << "}"; return ostr; } template istream& operator >> (istream& istr, pair<_KTy, _Ty>& m) { istr >> m.first >> m.second; return istr; } template istream& operator >> (istream& istr, vector<_Ty>& v) { for (size_t i = 0; i < v.size(); i++) istr >> v[i]; return istr; } namespace aux { // print tuple template struct tp { static void print(ostream& os, const Ty& v) { os << get(v) << ", "; tp::print(os, v); } }; template struct tp { static void print(ostream& os, const Ty& value) { os << get(value); } }; } template ostream& operator<<(ostream& os, const tuple& t) { os << "{"; aux::tp, 0, sizeof...(Tys)-1>::print(os, t); os << "}"; return os; } template inline void Fill(A(&array)[N], const T &val) { std::fill((T*)array, (T*)(array + N), val); } void dump_func() { DUMPOUT << endl; } template void dump_func(Head&& head, Tail&&... tail) { DUMPOUT << head; if (sizeof...(Tail) == 0) { DUMPOUT << " "; } else { DUMPOUT << ", "; } dump_func(std::move(tail)...); } #define PI 3.14159265358979323846 #define EPS 1e-11 #define FOR(i,a,b) for(int i=(a);i<(b);++i) #define REP(i,n) FOR(i,0,n) #define all(x) (x).begin(), (x).end() #define SZ(x) ((int)(x).size()) #define fake false int main() { //clock_t start, end; //start = clock(); //cin.tie(0); //ios::sync_with_stdio(false); int N, M; cin >> N >> M; vector> G(N); REP(i, M) { int a, b; cin >> a >> b; G[a].push_back(b); G[b].push_back(a); } { int count = 0; vector used(N, false); queue qu; qu.push(0); while (!qu.empty()) { int x = qu.front(); qu.pop(); if (used[x]) continue; used[x] = true; count++; for (int i = 0; i < G[x].size(); i++) qu.push(G[x][i]); } if (count != N) { cout << "NO" << endl; return 0; } } int odd_edge = 0; for (int i = 0; i < G.size(); i++) { odd_edge += G[i].size() % 2; } if (odd_edge == 0 || odd_edge == 2) cout << "YES" << endl; else cout << "NO" << endl; //end = clock(); //printf("%d msec.\k", end - start); return 0; }