#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vint;
typedef pair<int,int> pint;
typedef vector<pint> vpint;
#define rep(i,n) for(int i=0;i<(n);i++)
#define REP(i,n) for(int i=n-1;i>=(0);i--)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
#define all(v) (v).begin(),(v).end()
#define eall(v) unique(all(v), v.end())
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define chmax(a, b) a = (((a)<(b)) ? (b) : (a))
#define chmin(a, b) a = (((a)>(b)) ? (b) : (a))
const int MOD = 1e9 + 7;
const int INF = 1e9;
const ll INFF = 1e18;

int Sa[300000], Sb[300000];
int memo[10100];
int imos[10100];
int main(void) {
	int N, M; cin >> N >> M;
	rep(i, M) cin >> Sa[i] >> Sb[i];
	rep(i, M) imos[Sa[i]]++, imos[Sb[i] + 1]--;
	rep(i, 10000) imos[i + 1] += imos[i];

	// 連結か見る
	int mi = INF, ma = 0;
	rep(i, M) {
		chmin(mi, Sa[i]), chmax(ma, Sb[i]);
	}
	// printf("%d %d \n", mi, ma);
	bool f = true;
	reps(i, mi, ma + 1) if(imos[i] == 0) f = false;
	if(!f) {
		printf("No\n"); return 0;
	}
	rep(i, M) memo[Sa[i]]++, memo[Sb[i]]++;
	int cnt = 0;
	rep(i, N) if(memo[i] % 2) cnt++;
	if(cnt == 2) printf("YES\n");
	else printf("NO\n");
	
	// printf("YES\n");
	return 0;
}