#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; using ll = long long; using P = pair; constexpr int INF = 1001001001; constexpr int mod = 1000000007; // constexpr int mod = 998244353; template inline bool chmax(T& x, T y){ if(x < y){ x = y; return true; } return false; } template inline bool chmin(T& x, T y){ if(x > y){ x = y; return true; } return false; } struct CountUnionFind{ int sz; // vertex number vector par; vector rank; vector cnt; CountUnionFind(int n) : sz(n) { par.resize(sz); rank.assign(sz, 0); cnt.assign(sz, 1); for(int i = 0; i < sz; ++i){ par[i] = i; } } int find(int x){ if(par[x] == x) return x; else return par[x] = find(par[x]); } bool same(int x, int y){ return find(x) == find(y); } bool unite(int x, int y){ x = find(x), y = find(y); if(x == y) return false; if(rank[x] < rank[y]){ par[x] = y; cnt[y] += cnt[x]; } else{ par[y] = x; cnt[x] += cnt[y]; if(rank[x] == rank[y]) ++rank[x]; } return true; } int get_cnt(int x){ return cnt[find(x)]; } }; int main(){ ios::sync_with_stdio(false); cin.tie(nullptr); int N, M; cin >> N >> M; vector> graph(N); CountUnionFind uf(N); for(int i = 0; i < M; ++i){ int u, v; cin >> u >> v; graph[u].emplace_back(v); graph[v].emplace_back(u); uf.unite(u, v); } int vcnt = 0, oddcnt = 0; for(int i = 0; i < N; ++i){ vcnt += graph[i].size() > 0; oddcnt += graph[i].size() % 2 == 1; } for(int i = 0; i < N; ++i){ if(graph[i].size()){ if(uf.get_cnt(uf.find(i)) != vcnt){ cout << "NO\n"; return 0; } break; } } if(oddcnt == 0 || oddcnt == 2) cout << "YES\n"; else cout << "NO\n"; return 0; }