fn.cpp
#include <iostream>
#include <vector>
#include <stdio.h>
int main()
{
bool yn = false;
int body = 0;
int cary = 0;
int i;
//int poleCar[cary][2] = {(0,1),(0,2),(0,3),(0,4)};
//int poleBodu[body] = {0,0,0,0,0};
int x;
int y;
scanf("%d %d",&body,&cary);
std::vector<std::vector<int> > myVector(cary);
for(i = 0; i < cary;i++)
{
getchar();
scanf("%d %d",&x,&y);
myVector[i].push_back(x);
myVector[i].push_back(y);
}
std::vector<int> bodyVector;
for(i = 0;i<body;i++)
bodyVector.push_back(0);
for(i = 0;i<cary;i++)
{
bodyVector[myVector[i][0]]++;
bodyVector[myVector[i][1]]++;
}
for(i = 0;i<body;i++)
{
if(bodyVector[i] == 4)
{
std::cout << "YES" << std::endl;
return 0;
}
}
std::cout << "NO" << std::endl;
return 0;
}