#include "bits/stdc++.h" #define ALL(obj) (obj).begin(),(obj).end() #define RALL(obj) (obj).rbegin(),(obj).rend() #define REP(i, n) for(int i = 0; i < (int)(n); i++) #define REPR(i, n) for(int i = (int)(n); i >= 0; i--) #define FOR(i,n,m) for(int i = (int)(n); i < int(m); i++) using namespace std; typedef long long ll; const int MOD = 1e9 + 7; const int INF = MOD - 1; const ll LLINF = 4e18; //UnionFind class UnionFind { private: vector par; public: UnionFind(int n) { par.resize(n, -1); } int root(int x) { if (par[x] < 0) return x; return par[x] = root(par[x]); } bool unite(int x, int y) { int rx = root(x); int ry = root(y); if (rx == ry) return false; if (size(rx) < size(ry)) swap(rx, ry); par[rx] += par[ry]; par[ry] = rx; return true; } bool same(int x, int y) { int rx = root(x); int ry = root(y); return rx == ry; } int size(int x) { return -par[root(x)]; } }; int main() { int n, m; cin >> n >> m; UnionFind uni(n); vector> G(n); REP(i, m) { int a, b; cin >> a >> b; G[a].push_back(b); G[b].push_back(a); uni.unite(a, b); } int r = -INF; REP(i, n) { if (uni.size(i) > 1) { cout << i << endl; if (r == -1) { r == uni.root(i); } else if (r != uni.root(i)) { puts("NO"); return 0; } } } int cnt = 0; REP(i, n) { if (G[i].size() % 2 != 0) { cnt++; } } if (cnt == 2 || cnt == 0) { puts("YES"); } else { puts("NO"); } getchar(); getchar(); }