#include <iostream>
#include <vector>

using namespace std;

bool fl=false;
void dfs(int v, vector <vector <int> > &graph, vector <bool> &visited, vector <int> &value, int prev) {
    visited[v] = true;
    value[v]=prev;
    for (int i = 0; i < (int)graph[v].size(); ++i) {
        if(graph[v][i]){
            if(value[i]!=0 && value[i]%2==value[v]%2){
                fl=true;
                return;
            }
        }
        if (graph[v][i] && !visited[i]) {
            dfs(i, graph, visited, value, prev+1);
        }
    }

}

int main() {
    int n, m;
    cin>>n>>m;
    vector <vector<int> > graph(n, vector <int>(n));
    vector <bool> visited(n, 0);
    vector <bool> used(n, 0);
    vector <int> value(n, 0);

    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            if(i==j){
                graph[i][j]=false;
            }
        }
    }

    int a,b;
    for(int i=0;i<m;i++){
        cin>>a>>b;
        graph[a-1][b-1]=true;
        graph[b-1][a-1]=true;
        used[a-1]=true;
        used[b-1]=true;
    }

    while(1){
        int h=0;
        for(int i=0;i<n;i++){
            if(used[i] && !visited[i]){
                h++;
                dfs(i, graph, visited, value, 1);
                if(fl){
                    cout<<"NO";
                    return 0;
                }
            }
        }
        if(h==0){
            break;
        }
    }
    cout<<"YES";
}