#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main(){

    int station;
    int strain;
    int start, end;
    vector<int> stationflag;
    vector<int> startArray;
    vector<int> endArray;
    bool startendflag = false;
    int odd=0;
    int even=0;
    int max;
    int min;
    int vectMax, vectMin;

    cin>>station>>strain;
    stationflag.resize(station);
    startArray.resize(strain);
    endArray.resize(strain);
    max=0;
    min=station-1;

    for(int i=0; i<strain; ++i)
    {
        cin>>start>>end;
        stationflag[start]++;
        stationflag[end]++;
        *(startArray.data()+i)=start;
        *(endArray.data()+i)=end;
        if(min>start && max<end)
        {
            min=start;
            max=end;
        }
    }

    vectMin = *min_element(startArray.begin(), startArray.end());
    vectMax = *max_element(endArray.begin(), endArray.end());
    if(vectMin == min && vectMax == max)
        startendflag = true;

    for(int i=0; i<station; ++i)
    {
        if(stationflag[i] % 2 == 0)
            even++;
        else
            odd++;
    }

    if(station%2==0)
    {
        if(odd==2)
            cout<<"YES"<<endl;
        else if(odd==0)
        {
            if(startendflag)
                cout<<"YES"<<endl;
            else
                cout<<"NO"<<endl;
        }
        else
            cout<<"NO"<<endl;

    }
    else
    {
        if(odd==2 || odd==0)
            cout<<"YES"<<endl;
        else
            cout<<"NO"<<endl;
    }


    return 0;
}