#include <bits/stdc++.h>

using namespace std;

int g[110][100];
int c[110];
int n, m, f;


int main()
{

    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);

    int a, b;
    cin >> n >> m;
    f = 0;
    if(n==0||m==0)
    {
        cout << "YES";
        return 0;
    }
    for(int i = 0; i < m; i++)
    {
        cin >> a >> b;
        a--;
        b--;
        g[a][b]+=1;
        g[b][a]+=1;
    }
    for(int i = 0; i < n; i++)
    {
        c[i]=-1;
        g[i][i]=0;
    }
    for(int i = 0; i < n; i++)
    {
        if (c[i]==-1)
        {
            queue <int> q;
            q.push(i);
            c[i]=2;
            int v;
            while(!q.empty())
            {
                v = q.front();
                q.pop();
                for(int ii = 0 ; ii < n; ii++)
                {
                    if(g[v][ii]!=0)
                    {
                        if(c[ii]==-1)
                        {
                            c[ii]=3-c[v];
                            q.push(ii);
                        }
                        else if (c[ii]==c[v])
                        {
                            cout << "NO ";
                            return 0;
                        }
                    }
                }
            }
        }
    }
    cout << "YES" << endl;
}