fn.cpp
#include <cstdio>
void printarr( int * arr, int len )
{
for( int i = 0; i < len; i++ )
printf( "%d ", arr[i] );
printf( "\n" );
}
int main()
{
int n,m;
while( scanf("%d %d\n", &n, &m) == 2 )
{
bool yes = false;
int arr[n+1];
for( int i = 0; i < n+1; i++ ) arr[i] = 0;
for( int i = 0; i < m; i++ )
{
int a, b;
scanf( "%d %d\n", &a,&b );
arr[a] ++;
arr[b] ++;
//printarr( arr, n+1 );
if( !yes && (arr[a] == 4 || arr[b] == 4) )
{
yes = true;
printf( "YES\n" );
}
}
if( !yes ) printf( "NO\n" );
}
return 0;
}