# Pairs

## 题目描述

Toad Ivan has $m$ pairs of integers, each integer is between $1$ and $n$ , inclusive. The pairs are $(a_1, b_1), (a_2, b_2), \ldots, (a_m, b_m)$ . He asks you to check if there exist two integers $x$ and $y$ ( $1 \leq x < y \leq n$ ) such that in each given pair at least one integer is equal to $x$ or $y$ .

## 输入输出格式

### 输入格式

The first line contains two space-separated integers $n$ and $m$ ( $2 \leq n \leq 300\,000$ , $1 \leq m \leq 300\,000$ ) — the upper bound on the values of integers in the pairs, and the number of given pairs. The next $m$ lines contain two integers each, the $i$ -th of them contains two space-separated integers $a_i$ and $b_i$ ( $1 \leq a_i, b_i \leq n, a_i \neq b_i$ ) — the integers in the $i$ -th pair.

### 输出格式

Output "YES" if there exist two integers $x$ and $y$ ( $1 \leq x < y \leq n$ ) such that in each given pair at least one integer is equal to $x$ or $y$ . Otherwise, print "NO". You can print each letter in any case (upper or lower).

4 6
1 2
1 3
1 4
2 3
2 4
3 4

NO

5 4
1 2
2 3
3 4
4 5

YES

300000 5
1 2
1 2
1 2
1 2
1 2

YES

## 说明

In the first example, you can't choose any $x$ , $y$ because for each such pair you can find a given pair where both numbers are different from chosen integers. In the second example, you can choose $x=2$ and $y=4$ . In the third example, you can choose $x=1$ and $y=2$ .