#include <bits/stdc++.h>
#include <sys/time.h>
using namespace std;

#define rep(i,n) for(long long i = 0; i < (long long)(n); i++)
#define pb push_back
using ll = long long; using vll = vector<ll>; using vvll = vector<vll>;

struct UnionFind {
    vector<int> data;
    UnionFind(int size) : data(size, -1) { }
    // x, yをマージ, O(A^-1)
    bool unite(int x, int y) {
        x = root(x); y = root(y);
        if (x != y) {
            if (data[y] < data[x]) swap(x, y);
            data[x] += data[y]; data[y] = x;
        }
        return x != y;
    }
    // x, yが同じ集合なら1, O(A^-1)
    bool find(int x, int y) {
        return root(x) == root(y);
    }
    // xの根を探す。同じ集合なら同じ根が帰る, O(A^-1)
    int root(int x) {
        return data[x] < 0 ? x : data[x] = root(data[x]);
    }
};

int main(void) {
    ll n, m; cin >> n >> m;
    assert(n >= 2);
    assert(n <= 500);
    assert(m >= 1);
    assert(m <= n*(n-1)/2);

    vvll g(n);
    UnionFind uf(n);

    set<ll> vs;
    rep(i, m) {
        ll u, v; cin >> u >> v;
        assert(0 <= u && u <= n - 1);
        assert(0 <= v && v <= n - 1);
        g[u].pb(v);
        g[v].pb(u);
        vs.insert(u);
        vs.insert(v);
        uf.unite(u, v);
    }
    for (auto x : vs) {
        if (!uf.find(*vs.begin(), x)) {
            cout << "NO" << endl;
            return 0;
        }
    }
    ll ret = 0;
    rep(i, n) 
        ret += g[i].size() & 1;

    cout << (ret == 0 || ret == 2 ? "YES" : "NO") << endl;
    
    return 0;
}