#include <bits/stdc++.h>
#define rep(i,n)for(int i=0;i<(n);i++)
using namespace std;

int cnt[500];
class UnionFind {
	vector<int>par, high;
public:
	UnionFind(int n) {
		par = high = vector<int>(n);
		for (int i = 0; i < n; i++)par[i] = i;
	}
	int find(int x) {
		if (par[x] == x)return x;
		return par[x] = find(par[x]);
	}
	void unite(int x, int y) {
		x = find(x); y = find(y);
		if (x == y)return;
		if (high[x] > high[y])par[y] = x;
		else {
			par[x] = y;
			if (high[x] == high[y])high[y]++;
		}
	}
	bool same(int x, int y) {
		return find(x) == find(y);
	}
};
int main(){
	int n,m;scanf("%d%d",&n,&m);
	UnionFind uf(n);
	rep(i,m){
		int a,b;scanf("%d%d",&a,&b);
		cnt[a]++;cnt[b]++;
		uf.unite(a,b);
	}
	int c=0,d=0;
	rep(i,n){
		if(cnt[i]%2)c++;
		else d++;
	}
	int t=0;
	rep(i,n){
		if(cnt[i]==0)t++;
	}
	rep(i,n){
		int cnt=0;
		rep(j,n){
			if(uf.same(i,j))cnt++;
		}
		if(cnt!=1&&cnt!=n-t){
			puts("NO");
			return 0;
		}
	}
	if(c==0||c==2)puts("YES");
	else puts("NO");
}