#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
#include <iterator>
using namespace std;

int main()
{
    int n, m;
    cin >> n >> m;
    vector<bool> v(n, false);
    int cnt = 0;
    for(int i=0; i<2*m; ++i){
        int a;
        cin >> a;
        if(v[a]){
            -- cnt;
            v[a] = false;
        }
        else{
            ++ cnt;
            v[a] = true;
        }
    }

    if(cnt <= 2)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;

    return 0;
}