#include <iostream>
#include <cstdio>
#include <vector>
#include <cmath>
#include <cstring>
#include <numeric>
#include <algorithm>
#include <functional>
#include <array>
#include <map>
#include <queue>
#include <limits.h>
#include <set>
#include <stack>

using namespace std;

#define Getsign(n) ((n > 0) - (n < 0))
#define QWERTYR(c) (c == 'y' || c == 'u' || (c >= 'h' && c <= 'p') ?	true : false)
map<string, int> roma_time = { { "I",1 },{ "II",2 },{ "III",3 },{ "IIII",4 },{ "V",5 },{ "VI",6 },{ "VII",7 },{ "VIII",8 },{ "IX",9 },{ "X",10 },{ "XI",11 },{ "XII",12 } };

typedef vector<int> Ivec;
typedef pair<int, int> pii;

int main() {
	int n, m;
	scanf("%d %d", &n, &m);
	vector<vector<int>> graph(n, vector<int>());
	for (int i = 0; m > i; i++) {
		int a, b;
		scanf("%d %d", &a, &b);
		a--;
		b--;
		graph[a].push_back(b);
		graph[b].push_back(a);
	}

	queue<int> que;
	array<bool, 20000> tesu;
	for (int i = 0; n > i; i++) {
		tesu[i] = false;
	}
	for (int i = 0; graph[0].size() > i; i++) {
		que.push(graph[0][i]);
	}
	while (!que.empty()) {
		int vertex = que.front();
		que.pop();
		
		if (tesu[vertex]) {
			for (int i = 0; graph[vertex].size() > i; i++) {
				int tar = graph[vertex][i];
				if (tesu[tar]) {
					printf("YES\n");
					return 0;
				}
			}
		}
		else {
			for (int i = 0; graph[vertex].size() > i; i++) {
				tesu[graph[vertex][i]] = true;
				que.push(graph[vertex][i]);
			}
		}
	}

	printf("NO\n");
	return 0;
}