#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,fma,abm,mmx,avx,avx2")
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rrep(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define all(x) (x).begin(), (x).end()
#define sz(x) int(x.size())
#define yn(joken) cout<<((joken) ? "Yes" : "No")<<"\n"
#define YN(joken) cout<<((joken) ? "YES" : "NO")<<"\n"
using namespace std;
using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using vs = vector<string>;
using vc = vector<char>;
using vd = vector<double>;
using vld = vector<long double>;
using vvi = vector<vector<int>>;
using vvl = vector<vector<ll>>;
using vvs = vector<vector<string>>;
using vvc = vector<vector<char>>;
using vvd = vector<vector<double>>;
using vvld = vector<vector<long double>>;
using vvvi = vector<vector<vector<int>>>;
using vvvl = vector<vector<vector<ll>>>;
using vvvvi = vector<vector<vector<vector<int>>>>;
using vvvvl = vector<vector<vector<vector<ll>>>>;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
const int INF = 1e9;
const ll LINF = 2e18;
template <class T>
bool chmax(T& a, const T& b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
bool chmin(T& a, const T& b) {
    if (b < a) {
        a = b;
        return 1;
    }
    return 0;
}
bool ispow2(int i) { return i && (i & -i) == i; }
bool ispow2(ll i) { return i && (i & -i) == i; }
template <class T>
vector<T> make_vec(size_t a) {
    return vector<T>(a);
}
template <class T, class... Ts>
auto make_vec(size_t a, Ts... ts) {
    return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}
template <typename T>
istream& operator>>(istream& is, vector<T>& v) {
    for (int i = 0; i < int(v.size()); i++) {
        is >> v[i];
    }
    return is;
}
template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    for (int i = 0; i < int(v.size()); i++) {
        os << v[i];
        if (i < int(v.size()) - 1) os << ' ';
    }
    return os;
}

static uint32_t RandXor(){
    static uint32_t x=123456789;
    static uint32_t y=362436069;
    static uint32_t z=521288629;
    static uint32_t w=88675123;
    uint32_t t;
 
    t=x^(x<<11);
    x=y; y=z; z=w;
    return w=(w^(w>>19))^(t^(t>>8));
}

static double Rand01(){
    return (RandXor()+0.5)*(1.0/UINT_MAX);
}

template <typename T = int>
struct Edge{
    int from, to;
    T cost;
    int idx;
    Edge() = default;
    Edge(int from, int to, T cost = 1, int idx = -1) : from(from), to(to), cost(cost), idx(idx) {}
    operator int() const { return to; }
};

template <typename T = int>
struct Graph{
    vector<vector<Edge<T>>> g;
    int es;
    Graph() = default;
    explicit Graph(int n) : g(n), es(0) {}
    size_t size() const{
        return g.size();
    }

    void add_directed_edge(int from, int to, T cost = 1){
        g[from].emplace_back(from, to, cost, es++);
    }

    void add_edge(int from, int to, T cost = 1){
        g[from].emplace_back(from, to, cost, es);
        g[to].emplace_back(to, from, cost, es++);
    }

    void read(int M, int padding = 0, bool weighted = false, bool directed = false){
        for (int i = 0; i < M; i++){
            int a, b;
            cin >> a >> b;
            a += padding;
            b += padding;
            T c = T(1);
            if (weighted) cin >> c;
            if (directed) add_directed_edge(a, b, c);
            else add_edge(a, b, c);
        }
    }

    inline vector<Edge<T>> &operator[](const int &k){
        return g[k];
    }

    inline const vector<Edge<T>> &operator[](const int &k) const{
        return g[k];
    }
};

template <typename T = int>
using Edges = vector<Edge<T>>;

// GetEulerianTrail(Graph<int> G,int N,bool directed)
// ->N:頂点数, Gのオイラー路/閉路を返す, 存在しない場合は空の配列を返す, 有向グラフならdirected=trueとする
template <typename graph>
vector<int> GetEulerianTrail(graph &_G,int N,const bool directed) {
    vector<int> trail;

    if(directed){
        vector<int> in(N),out(N);
        for(int v=0;v<N;v++){
            for(auto nv:_G[v]){
                in[nv]++;
                out[v]++;
            }
        }
        int s=-1,t=-1;
        for(int v=0;v<N;v++){
            if(in[v]==out[v]) ;
            else if(in[v]==out[v]+1){
                if(t!=-1) return trail;
                t=v;
            }
            else if(in[v]+1==out[v]){
                if(s!=-1) return trail;
                s=v;
            }
            else return trail;
        }
        graph G=_G;
        function<void(int, vector<int> &)> dfs=[&](int u, vector<int> &trail) {
                while(!G[u].empty()) {
                        int v=G[u].back();
                        G[u].pop_back();
                        dfs(v,trail);
                }
                trail.emplace_back(u);
        };
        dfs(s, trail);
        reverse(trail.begin(), trail.end());
        return trail;
    }
    else{
        vector<int> odd;
        for(int v=0;v<N;v++) if(int(_G[v].size())&1) odd.emplace_back(v);
        if(int(odd.size())>2) return trail;
        int s=(odd.empty() ? 0 : odd[0]);
        vector<multiset<int>> G(N);
        for(int v=0;v<N;v++) for(auto nv:_G[v]) G[v].emplace(nv);
        function<void(int, vector<int> &)> dfs=[&](int u, vector<int> &trail) {
                while(!G[u].empty()) {
                        auto it=G[u].begin();
                        int nv=*it;
                        G[nv].erase(G[nv].find(u));
                        G[u].erase(it);
                        dfs(nv,trail);
                }
                trail.emplace_back(u);
        };
        dfs(s, trail);
        reverse(trail.begin(), trail.end());
        return trail;
    }
}

// merge(x,y):mergeする,未併合ならtrueが,併合済みならfalseが返ってくる
// leader(x):xの根を返す
// size(x):xの属する集合のサイズを返す
// same(x,y):x,yが同じ集合に属するかどうか
// groups():各集合に含まれる要素を返す

struct dsu{
public:
    dsu() : _n(0) {}
    dsu(int n) : _n(n), parent_or_size(n, -1) {}

    int merge(int a, int b){
        assert(0 <= a && a < _n);
        assert(0 <= b && b < _n);
        int x = leader(a), y = leader(b);
        if (x == y)
            return x;
        if (-parent_or_size[x] < -parent_or_size[y])
            swap(x, y);
        parent_or_size[x] += parent_or_size[y];
        parent_or_size[y] = x;
        return x;
    }

    bool same(int a, int b){
        assert(0 <= a && a < _n);
        assert(0 <= b && b < _n);
        return leader(a) == leader(b);
    }

    int leader(int a){
        assert(0 <= a && a < _n);
        if (parent_or_size[a] < 0)
            return a;
        return parent_or_size[a] = leader(parent_or_size[a]);
    }

    int size(int a){
        assert(0 <= a && a < _n);
        return -parent_or_size[leader(a)];
    }

    vector<vector<int>> groups(){
        vector<int> leader_buf(_n), group_size(_n);
        for (int i = 0; i < _n; i++){
            leader_buf[i] = leader(i);
            group_size[leader_buf[i]]++;
        }
        vector<vector<int>> result(_n);
        for (int i = 0; i < _n; i++){
            result[i].reserve(group_size[i]);
        }
        for (int i = 0; i < _n; i++){
            result[leader_buf[i]].push_back(i);
        }
        result.erase(
            remove_if(result.begin(), result.end(),
                           [&](const vector<int> &v)
                           { return v.empty(); }),
            result.end());
        return result;
    }

private:
    int _n;
    // root node: -1 * component size
    // otherwise: parent
    vector<int> parent_or_size;
};

void solve(){
    int N,M;
    cin>>N>>M;
    Graph<int> G(N);
    dsu UF(N);
    rep(_,M){
        int a,b;
        cin>>a>>b;
        G.add_edge(a,b);
        UF.merge(a,b);
    }
    int cnt=0;
    for(auto elm:UF.groups()) if(sz(elm)>1) cnt++;
    if(cnt!=1){
        cout<<"NO\n";
        return;
    }
    auto ret=GetEulerianTrail(G,N,false);
    YN(sz(ret));
}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    solve();
}