#include <iostream>
#include <vector>

using namespace std;

vector<vector<int>> graph;

void dfs(int v, int num) {
    color[v] = num;
    for (int to : graph[v]) {
        if (color[to] == 0) {
            dfs(to, (num * -1));
        } else if (color[to] == num) {
            cout << "NO" << endl;
            exit(0);
        }
    }
}

int main() {
    int n, m, a, b;
    cin >> n >> m;
    graph.resize(n + 1);
    color.assign(n + 1, 0);
    for (int j = 0; j < m; j++) {
        cin >> a >> b;
        --a;
        --b;
        graph[a].push_back(b);
        graph[b].push_back(a);
    }
    for (int i = 0; i < n; i++) {
        if (color[i] == 0) {
            dfs(i, 1);
        }
    }
    cout << "YES" << endl;
}