#include "bits/stdc++.h"
using namespace std;
#define int long long
#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, a, b) for(int i=(b-1);i>=(a);i--)
#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define ALL(a) (a).begin(),(a).end()
#define UNIQUE_SORT(l) sort(ALL(l)); l.erase(unique(ALL(l)), l.end());
#define CONTAIN(a, b) find(ALL(a), (b)) != (a).end()
#define array2(type, x, y) array<array<type, y>, x>
#define vector2(type) vector<vector<type> >
#define out(...) printf(__VA_ARGS__)

int dxy[] = {0, 1, 0, -1, 0};

/*================================*/

int N, M;

signed main()
{
#if DEBUG
    std::ifstream in("input.txt");
    std::cin.rdbuf(in.rdbuf());
#endif
    cin >> N >> M;
    int S[N], T[N];
    REP(i, N) S[i] = 0;
    REP(i, N) T[i] = 0;
    int a, b;
    REP(i, M) {
        cin >> a >> b;
        S[a]++;
        S[b]++;
        FOR(j, a, b) {
            T[j] = 1;
        }
    }
    int odd = 0;
    REP(i, N) if (S[i] % 2 == 1) odd++;
    
    bool ok = (odd <= 2);
    
    REP(i, N-1) if (!T[i]) ok = false;
    
    if (!ok) {
        cout << "NO" << endl;
    } else {
        cout << "YES" << endl;
    }
    
    return 0;
}