#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define _USE_MATH_DEFINES #include #include using namespace std; inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; } template inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); } template inline T sqr(T x) { return x*x; } typedef vector vi; typedef vector vvi; typedef vector vll; typedef vector vs; typedef pair pii; typedef long long ll; typedef unsigned long long ull; //repetition //------------------------------------------ #define FOR(i,a,b) for(int i=(a);i<(b);++i) #define rep(i,n) FOR(i,0,n) #define P(p) cout<<(p)< >(a, vector(b, 0)) #define ALL(a) (a).begin(),(a).end() #define RALL(a) (a).rbegin(), (a).rend() #define pb push_back #define mp make_pair #define INF (1000000000) #define SZ(a) int((a).size()) #define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i) #define EXIST(s,e) ((s).find(e)!=(s).end()) #define SORT(c) sort((c).begin(),(c).end()) #define MOD 1000000007LL #define FSP(a) cout << fixed << setprecision(a) template T gcd(T x, T y) { if (y == 0) return x; else return gcd(y, x%y); } template T lcm(T a, T b) { return a / gcd(a, b) * b; } template bool is_prime(T n) { for (int i = 2; i * i <= n; i++) { if (n % i == 0) return false; } return n != 1; } map prime_factor(int n) { map res; for (int i = 2; i * i <= n; i++) { while (n % i == 0) { ++res[i]; n /= i; } } if (n != 1) res[n] = 1; return res; } int extgcd(int a, int b, int& x, int& y) {// int d = a; if (b != 0) { d = extgcd(b, a%b, y, x); y -= (a / b)*x; } else { x = 1; y = 0; } return d; } ll mod_pow(ll x, ll n, ll mod) { if (n == 0) return 1; ll res = mod_pow(x * x % mod, n / 2, mod); if (n & 1) res = res * x % mod; return res; } vector split(const string &str, char delim) { vector res; size_t current = 0, found; while ((found = str.find_first_of(delim, current)) != string::npos) { res.push_back(string(str, current, found - current)); current = found + 1; } res.push_back(string(str, current, str.size() - current)); return res; } bool is_kadomatsu(int a, int b, int c) { if (a == b || a == c || b == c)return false; if (a > b && c > b) return true; if (a < b && c < b)return true; return false; } struct UF { int n; vi d; UF() {} UF(int n) :n(n), d(n, -1) {} int root(int v) { if (d[v] < 0) return v; return d[v] = root(d[v]); } bool same(int a, int b) { return root(a) == root(b); } bool unite(int x, int y) { x = root(x); y = root(y); if (x == y) return false; if (size(x) < size(y)) swap(x, y); d[x] += d[y]; d[y] = x; return true; } int size(int v) { return -d[root(v)]; } }; vector divisor(int n) { if (n == 1) return{}; vi res; for (int i = 1; i*i <= n; i++) { if (n%i == 0) { res.emplace_back(i); if (i != 1 && i != n / i)res.emplace_back(n / i); } } return res; } struct Bellmanford { int n; struct edge { int from, to, cost; }; vector E; vi d; Bellmanford(int n) :n(n), d(n) { E.resize(n); } void add_edge(int x, int y, int cost) { edge e; e.from = x; e.to = y; e.cost = cost; E.push_back(e); } void shortest_path(int s) { rep(i, n)d[i] = INF; d[s] = 0; while (true) { bool update = false; for (auto e : E) { if (d[e.from] != INF && d[e.to] > d[e.from] + e.cost) { d[e.to] = d[e.from] + e.cost; update = true; } } if (!update) break; } } }; struct Dijkstra { int n; struct edge { int to; ll cost; }; vector> G; vll d; Dijkstra(int n) :n(n), d(n) { G.resize(n); } void add_edge(int x, int y, ll cost) { edge e; e.to = y; e.cost = cost; G[x].push_back(e); } void shortest_path(int s) { rep(i, n)d[i] = 100000000000000000; d[s] = 0; priority_queue, vector>, greater>> que; que.push(make_pair(0, s)); while (!que.empty()) { pii p = que.top(); que.pop(); int v = p.second; if (d[v] < p.first) continue; for (auto e : G[v]) { if (d[e.to] > d[v] + e.cost) { d[e.to] = d[v] + e.cost; que.push(make_pair(d[e.to], e.to)); } } } } }; struct Segmenttree { int n; vector> dat; Segmenttree() {} void init(ll n_) { n = 1; while (n < n_) n *= 2; dat.resize(2 * n - 1); rep(i, 2 * n - 1)dat[i] = pair(-INF, -INF); } void update(int idx, ll val) { idx += n - 1; dat[idx] = make_pair(val, -(idx - n + 1)); while (idx > 0) { idx = (idx - 1) / 2; dat[idx] = max(dat[idx * 2 + 1], dat[idx * 2 + 2]); } } pair query(int a, int b) { return query_seg(a, b, 0, 0, n); } pair query_seg(int a, int b, int k, int l, int r) { if (r <= a || b <= l) return pair(-INF, -INF); if (a <= l && r <= b)return dat[k]; else { return max(query_seg(a, b, k * 2 + 1, l, (l + r) / 2), query_seg(a, b, k * 2 + 2, (l + r) / 2, r)); } } }; //------------------------------------------------------------- int main() { int n, m; cin >> n >> m; UF uf(n); int count[555]; memset(count, 0, sizeof(count)); rep(i, m) { int a, b; cin >> a >> b; count[a]++; count[b]++; uf.unite(a, b); } rep(i, n)rep(j, i) { if (count[i] == 0 || count[j] == 0) continue; if (!uf.same(i, j)) { P("NO"); return 0; } } int count1 = 0; rep(i, n) { if (count[i] % 2 != 0)count1++; } if (count1 == 0 || count1 == 2) { P("YES"); } else { P("NO"); } return 0; }