Problem:
Score : 200 points

Problem Statement

There are four towns, numbered 1,2,3 and 4.
Also, there are three roads. The i-th road connects different towns a_i and b_i bidirectionally.
No two roads connect the same pair of towns. Other than these roads, there is no way to travel between these towns, but any town can be reached from any other town using these roads.

Determine if we can visit all the towns by traversing each of the roads exactly once.

Constraints

1 \leq a_i,b_i \leq 4(1\leq i\leq 3)

a_i and b_i are different. (1\leq i\leq 3)

No two roads connect the same pair of towns.

Any town can be reached from any other town using the roads.

Input

Input is given from Standard Input in the following format:

a_1 b_1
a_2 b_2
a_3 b_3

Output

If we can visit all the towns by traversing each of the roads exactly once, print YES; otherwise, print NO.

Sample Input 1

4 2
1 3
2 3

Sample Output 1

YES

We can visit all the towns in the order 1,3,2,4.

Sample Input 2

3 2
2 4
1 2

Sample Output 2

NO

Sample Input 3

2 1
3 2
4 3

Sample Output 3

YES

Solution in PHP (5.6.30) (judge verdict: Wrong Answer)

<?php


while ($line = fgets(STDIN)) {
   $tmp[] = trim($line);
}

// 配列の各要素をさらに分解します
foreach ($tmp as $key => $value) {
  $input[] = explode(" ", $value);
} 

// $input = array(2, 1, 3, 2, 4, 3); //N K

/*
アウトな例
・同じ街が３回でる ＝ 同じ数字が３つ以上
・出ない数字がある

*/
$count = array(
	1 => 0,
	2 => 0,
	3 => 0,
	4 => 0,
);
foreach ($input as $key => $townNum) {
	$count[$townNum]++;
}


$noFg = false; 
foreach ($count as $townNum => $countAppear) {
	if(2 < $countAppear || $countAppear == 0) {
		$noFg = true; 
	}
}

if(!$noFg) {
	print 'YES';
} else {
	print 'NO';
}