#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <cstring>
#include <map>
#include <queue>
#include <cmath>
#include <complex> // complex<double> a(1.2 , 2.3);// real(): 1.2, imag()2.3
using namespace std;

#define MOD 1000000007
#define ll long long
#define ld long double
#define FOR(i,a,b) for(ll i=(ll)a;i<(ll)b;i++)
#define rep(i,n) FOR(i,0,n)
#define pb push_back
#define mp make_pair
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define rmsame(a) sort(all(a)),a.erase(unique(all(a)), a.end())
#define rmvector(a,b) rep(i,a.size())rep(j,b.size())if(a[i]==b[j]){a.erase(a.begin()+i);i--;break;}
template<typename X> bool exist(vector<X> vec, X item){return find(all(vec), item)!=vec.end();}

ll station[501];


struct UnionFind {

  vector<int> node;
  UnionFind(int n) : node(n,-1) {}

  bool unite(int x, int y) {
    x = root(x); 
    y = root(y);
    if (x != y) {
      if (node[y] < node[x]) swap(x, y);
      node[x] += node[y]; 
      node[y] = x;
    }
    return x != y;
  }

  bool same(int x, int y) {
    return root(x) == root(y);
  }

  int root(int x) {
    return node[x] < 0 ? x : node[x] = root(node[x]);
  }

  int size(int x) {
    return -node[root(x)];
  }
    
};

void operat(ll a){
  if(station[a]==0) station[a]=1;
  else station[a]=0;
}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll N , M;
  cin >> N >> M;
  UnionFind road(501);
  vector<ll> direction;
    
  rep(i,M){
    ll a, b; cin >> a >> b;
    operat(a);
    operat(b);
    road.unite(a,b);
    direction.pb(a);
    direction.pb(b);

  }

  ll ans = 0;
  rep(i,501){
    if(station[i]!=0) ans ++;
    
  }

  ll R = road.root(direction[0]);
  rep(i,direction.size()-1){
    if(road.root(direction[i+1]) != R){
      cout << "NO" << endl;
      return 0;
    }
  }
  
  

  if(ans == 2 || ans == 0) cout << "YES" << endl;
  else cout << "NO" << endl;
  //cout << fixed << setprecision(16) << ans << endl;
  return 0;
}