#include <iostream>
#include <vector>
#include <queue>
using namespace std;
int main()
{
    int a,b,x,y;
    cin>>b;
    cin>>a;
    vector<int>par[b];
    int boja[b];
    for(int i=0;i<a;i++)
    {
        cin>>x>>y;
        par[x].push_back(y);
        par[y].push_back(x);
    }
    for(int i=0;i<b;i++)
    {
        boja[i]=-1;
    }
    bool t=false;
    queue<int>Q;
    Q.push(0);
    boja[0]=0;
    while(!Q.empty())
    {
        int teme=Q.front();
        Q.pop();
        if(t==true)
        {
            cout<<"NO";
            return 0;
        }
        for(int i=0;i<par[teme].size();i++)
        {
            int sosed=par[teme][i];
            int boja_za_sleden_sosed = -1;
            if(boja[teme] == 0) {
                boja_za_sleden_sosed = 1;
            }
            else {
                boja_za_sleden_sosed = 0;
            }
            if(boja[sosed] == -1) {
                boja[sosed] =  boja_za_sleden_sosed;
                Q.push(sosed);
            }
            else if(boja[sosed] == boja[teme]) {
                t = true;
                break;
            }
        }
    }
    if(t==false)
    {
        cout<<"YES" << endl;
    }
    else {
        cout << "NO" << endl;
    }
    return 0;
    }