// competitive-verifier: PROBLEM https://onlinejudge.u-aizu.ac.jp/problems/0225
#include <iostream>
#include <set>
template <class T>
struct flip_set {
    flip_set() : data() {}
    const auto begin() const { return data.begin(); }
    auto begin() { return data.begin(); }
    const auto end() const { return data.end(); }
    auto end() { return data.end(); }
    bool empty() const { return data.empty(); }
    int size() const { return data.size(); }
    bool contains(const T &x) const { return data.count(x); }
    bool contains(T &&x) const { return data.count(std::move(x)); }
    bool flip(const T &x) {
        if (data.count(x)) return data.erase(x), false;
        else return data.emplace(x), true;
    }
    bool flip(T &&x) {
        if (data.count(x)) return data.erase(std::move(x)), false;
        else return data.emplace(x), true;
    }
  private:
    std::set<T> data;
};
#include <utility>
#include <vector>
/**
 * @brief 素集合データ構造
 * @details Implement (union by size) + (path compression)
 * @see https://github.com/atcoder/ac-library/blob/master/atcoder/dsu.hpp
 */
struct union_find {
    union_find() = default;
    explicit union_find(int _n) : _rank(_n), data(_n, -1) {}
    const int &operator[](std::size_t x) const { return data[x]; }
    int &operator[](std::size_t x) { return data[x]; }
    int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
    int get_root(int x) { return root(x); }
    bool is_root(int x) const { return data[x] < 0; }
    bool same(int x, int y) { return root(x) == root(y); }
    bool is_same(int x, int y) { return same(x, y); }
    int rank() { return _rank; }
    int size(int x) { return -(data[root(x)]); }
    int get_size(int x) { return size(x); }
    std::vector<int> leaders() {
        std::vector<int> res;
        for (int i = 0; i < (int)data.size(); ++i) {
            if (is_root(i)) res.emplace_back(i);
        }
        return res;
    }
    bool unite(int x, int y) {
        x = root(x), y = root(y);
        if (x == y) return false;
        --_rank;
        if (data[x] > data[y]) std::swap(x, y);
        data[x] += data[y];
        data[y] = x;
        return true;
    }
    template <class F>
    bool unite(int x, int y, F f) {
        x = root(x), y = root(y);
        if (x != y) {
            if (data[x] > data[y]) std::swap(x, y);
            data[x] += data[y];
            data[y] = x;
        }
        f(x, y);
        return x != y;
    }
  private:
    int _rank;
    std::vector<int> data;
};
int main(void) {
    int n, m;
    std::cin >> n >> m;
    flip_set<int> fs;
    std::set<int> st;
    union_find uf(n);
    while (m--) {
        int a, b;
        std::cin >> a >> b;
        fs.flip(a);
        fs.flip(b);
        st.emplace(a);
        st.emplace(b);
        uf.unite(a, b);
    }
    if (uf.size(*st.begin()) == (int)st.size() && fs.size() <= 2) {
        std::cout << "YES\n";
    } else {
        std::cout << "NO\n";
    }
    return 0;
}