fn.cpp
#include <algorithm>
#include <cctype>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
using namespace std;
#define DEBUG(x) cout << ">>> " << #x << " : " << x << endl;
#define REP(i,a) for (int i = 0; i < (a); ++i)
#define FOR(i,a,b) for (int i = (a); i <= (b); ++i)
#define FORD(i,a,b) for (int i = (a); i >= (b); --i)
inline bool EQ(double a, double b) { return fabs(a-b) < 1e-9; }
const int INF = 1<<29;
typedef long long ll;
///////////////////////////////////////////////////////////////////////////
const int MAX = 10007;
int N, M;
vector<int> graph[MAX];
int visited[MAX];
bool go(int node)
{
queue<int> manage;
manage.push(node);
visited[node] = true;
int sum = 0, root = node;
while (!manage.empty())
{
node = manage.front();
manage.pop();
int found = 0;
REP(i, graph[node].size())
{
int next = graph[node][i];
if (!visited[next])
{
manage.push(next);
visited[next] = true;
found += 1;
}
}
if (!found || (node==root && found==1)) sum += 1;
}
return sum >= 4;
}
int main()
{
while (scanf("%d%d", &N, &M) == 2)
{
REP(i, N) graph[i].clear();
REP(i, M)
{
int a, b;
scanf("%d%d", &a, &b);
--a, --b;
graph[a].push_back(b);
graph[b].push_back(a);
}
memset(visited, 0, sizeof(visited));
bool ok = false;
REP(i, N)
if (!visited[i])
ok = ok || go(i);
if (ok) printf("YES\n");
else printf("NO\n");
}
return 0;
}