fn.cpp

#include <cstdio>
#include <cmath>
#include <iostream>
#include <string>
#include <map>
#include <cstdlib>
 
using namespace std;
 
 
int main()
{
	int points, lines;
	while (scanf("%d %d", &points, &lines))
	{
		std::map<int, int> counts;
		bool x = false;
		while (lines--)
		{
			int f, s;
			scanf("%d %d", &f, &s);
			if (counts.find(f) == counts.end())
				counts[f] = 1;
			else
			{
				if (++counts[f] >= 4)
				{
					printf("YES\n");
					x = true;
					break;
				}
			}
 
			if (counts.find(s) == counts.end())
				counts[s] = 1;
			else
			{
				if (++counts[s] >= 4)
				{
					printf("YES\n");
					x = true;
					break;
				}
			}
		}
		if (!x)
			printf("NO\n");
	}
 
	return 0;
}