#include <bits/stdc++.h>
using namespace std;
#define LOCAL
#pragma region Macros
typedef long long ll;
#define ALL(x) (x).begin(),(x).end()
const long long MOD=1000000007;
// const long long MOD=998244353;
const int INF=1e9;
const long long IINF=1e18;
const int dx[4]={1,0,-1,0},dy[4]={0,1,0,-1};
const char dir[4]={'D','R','U','L'};

template<typename T>
istream &operator>>(istream &is,vector<T> &v){
    for (T &x:v) is >> x;
    return is;
}
template<typename T>
ostream &operator<<(ostream &os,const vector<T> &v){
    for (int i=0;i<v.size();++i){
        os << v[i] << (i+1==v.size()?"": " ");
    }
    return os;
}
template<typename T,typename U>
ostream &operator<<(ostream &os,const pair<T,U> &p){
    os << '(' << p.first << ',' << p.second << ')';
    return os;
}
template<typename T,typename U>
ostream &operator<<(ostream &os,const map<T,U> &m){
    os << '{';
    for (auto itr=m.begin();itr!=m.end();++itr){
        os << '(' << itr->first << ',' << itr->second << ')';
        if (++itr!=m.end()) os << ',';
        --itr;
    }
    os << '}';
    return os;
}
template<typename T>
ostream &operator<<(ostream &os,const set<T> &s){
    os << '{';
    for (auto itr=s.begin();itr!=s.end();++itr){
        os << *itr;
        if (++itr!=s.end()) os << ',';
        --itr;
    }
    os << '}';
    return os;
}

void debug_out(){cerr << '\n';}
template<class Head,class... Tail>
void debug_out(Head&& head,Tail&&... tail){
    cerr << head;
    if (sizeof...(Tail)>0) cerr << ", ";
    debug_out(move(tail)...);
}
#ifdef LOCAL
#define debug(...) cerr << " ";\
cerr << #__VA_ARGS__ << " :[" << __LINE__ << ":" << __FUNCTION__ << "]" << '\n';\
cerr << " ";\
debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

template<typename T> T gcd(T x,T y){return y!=0?gcd(y,x%y):x;}
template<typename T> T lcm(T x,T y){return x/gcd(x,y)*y;}

template<class T1,class T2> inline bool chmin(T1 &a,T2 b){
    if (a>b){a=b; return true;} return false;
}
template<class T1,class T2> inline bool chmax(T1 &a,T2 b){
    if (a<b){a=b; return true;} return false;
}
#pragma endregion

template<bool directed>
struct EulerianTrail{
    vector<vector<pair<int,int>>> G;
    vector<vector<int>> BG;
    vector<pair<int,int>> es;
    vector<int> used,visited,deg;
    EulerianTrail(int n):G(n),BG(n),visited(n,0),deg(n,0){}
    void add_edge(int u,int v){
        int m=es.size();
        es.emplace_back(u,v);
        used.emplace_back(0);
        BG[u].emplace_back(v);
        BG[v].emplace_back(u);
        G[u].emplace_back(v,m);
        ++deg[u];
        if (directed) --deg[v];
        else G[v].emplace_back(u,m),++deg[v];
    }
    void dfs(int v,int &s,int &t,int &check){
        visited[v]=1;
        if (directed){
            if (abs(deg[v])>1) check=0;
            else if (deg[v]==1){
                if (~s) check=0;
                else s=v;
            }
        } else {
            if (deg[v]&1){
                if (s<0) s=v;
                else if (t<0) t=v;
                else check=0;
            }
        }
        for (int u:BG[v]){
            if (visited[u]) continue;
            dfs(u,s,t,check);
        }
    }
    vector<int> go(int s){
        stack<pair<int,int>> st;
        vector<int> ord;
        st.emplace(s,-1);
        while(!st.empty()){
            int v=st.top().first;
            visited[v]=1;
            if (G[v].empty()){
                ord.emplace_back(st.top().second);
                st.pop();
            } else {
                auto e=G[v].back(); G[v].pop_back();
                if (used[e.second]) continue;
                used[e.second]=1;
                st.emplace(e);
            }
        }
        ord.pop_back();
        reverse(ord.begin(),ord.end());
        return ord;
    }
    vector<vector<int>> build(){
        for (int i=0;i<G.size();++i){
            if (directed&&deg[i]!=0) return {};
            if (!directed&&(deg[i]&1)) return {};
        }
        vector<vector<int>> res;
        for (int i=0;i<G.size();++i){
            if (G[i].empty()||visited[i]) continue;
            res.emplace_back(go(i));
        }
        return res;
    }
    vector<vector<int>> build_semi(){
        vector<vector<int>> res;
        for (int i=0;i<G.size();++i){
            if (visited[i]) continue;
            int s=-1,t=-1,check=1;
            dfs(i,s,t,check);
            if (!check) return {};
            res.emplace_back(go(~s?s:i));
            if (res.back().empty()) res.pop_back();
        }
        return res;
    }
    pair<int,int> operator[](int i){return es[i];}
};

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N,M; cin >> N >> M;

    EulerianTrail<false> ET(N);
    for (int i=0;i<M;++i){
        int a,b; cin >> a >> b;
        ET.add_edge(a,b);
    }

    cout << (ET.build_semi().size()==1?"YES":"NO") << '\n';
}