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;
}