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#include <iostream>
#include <queue>
#include <cstring>
using namespace std;
typedef long long ll;
int n, m;
vector<int> graph[1005];
int color[1005];
bool visited[1005];
bool dfs(int node) {
    for(int i = 0; i < graph[node].size(); i++) {
        int sosed = graph[node][i];
        if(!visited[sosed]) {
            visited[sosed] = true;
            color[sosed] = 1 - color[node];
            if(!dfs(sosed)) {
                return false;
            }
        }
        else if(color[sosed] == color[node]) {
            return false;
        }
    }
    return true;
}
int main() {
    ios_base::sync_with_stdio(false);
    cin >> n >> m;
    for(int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        graph[a].push_back(b);
        graph[b].push_back(a);
    }
    for(int i = 0; i <= n; i++) {
        color[i] = -1;
        visited[i] = false;
    }
    color[0] = 1;
    
    if(dfs(0)) {
        cout << "YES" << endl;
    }
    else {
        cout << "NO" << endl;
    }
    return 0;
}