B. Pairs

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该问题要求判断是否存在两个整数x和y（1≤x<y≤n），使得每对给定的整数中至少有一个等于x或y。输入包含n和m，表示数值范围和对数，然后给出m对不同的整数。输出'YES'如果存在这样的x和y，否则输出'NO'。示例展示了不同情况下的判断结果。

链接：https://codeforces.com/problemset/problem/1169/B

Toad Ivan has mm pairs of integers, each integer is between 11 and nn, inclusive. The pairs are (a1,b1),(a2,b2),…,(am,bm)(a1,b1),(a2,b2),…,(am,bm).

He asks you to check if there exist two integers xx and yy (1≤x<y≤n1≤x<y≤n) such that in each given pair at least one integer is equal to xx or yy.

Input

The first line contains two space-separated integers nn and mm (2≤n≤3000002≤n≤300000, 1≤m≤3000001≤m≤300000) — the upper bound on the values of integers in the pairs, and the number of given pairs.

The next mm lines contain two integers each, the ii-th of them contains two space-separated integers aiai and bibi (1≤ai,bi≤n,ai≠bi1≤ai,bi≤n,ai≠bi) — the integers in the ii-th pair.

Output

Output "YES" if there exist two integers xx and yy (1≤x<y≤n1≤x<y≤n) such that in each given pair at least one integer is equal to xx or yy. Otherwise, print "NO". You can print each letter in any case (upper or lower).

Examples

input

Copy

output

Copy

NO

input

Copy

output

Copy

YES

input

Copy

output

Copy

YES

Note

In the first example, you can't choose any xx, yy 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=2x=2 and y=4y=4.

In the third example, you can choose x=1x=1 and y=2y=2.

代码：

#include <bits/stdc++.h>
using namespace std;
long long t,n,m,k,s=0,x,y,p,q,max1=0,c,d;
long long a[1000001],b[1000001],vis[1000001]={0};
int main()
{
	cin>>n>>m;
	for(int i=1;i<=m;i++)
	{
		cin>>a[i]>>b[i];
	}
	x=a[1],y=b[1];
	int fl=0;
	for(int i=2;i<=m;i++)
	{
		if(a[i]!=x&&b[i]!=y&&a[i]!=y&&b[i]!=x)
		{
			p=a[i];
			q=b[i];
			fl=1;
			break;
		}
	}
	if(fl==1)
	c=x,d=p;
	else
	{
		cout<<"YES";
		return 0;
	}
	
	
	int flag=0;
	for(int i=1;i<=m;i++)
	{
		if(a[i]==c||b[i]==c||a[i]==d||b[i]==d)
		{
			continue;
		}
		else
		{
			flag=1;
			break;
		}
	}
	if(flag==0)
	cout<<"YES";
	else
	{
		c=x,d=q;
		flag=0;
		for(int i=1;i<=m;i++)
		{
			if(a[i]==c||b[i]==c||a[i]==d||b[i]==d)
			{
				continue;
			}
			else
			{
				flag=1;
				break;
			}
		}
		if(flag==0)
		cout<<"YES";
		else
		{
			c=y,d=q;
			flag=0;
			for(int i=1;i<=m;i++)
			{
				if(a[i]==c||b[i]==c||a[i]==d||b[i]==d)
				{
					continue;
				}
				else
				{
					flag=1;
					break;
				}
			}
			if(flag==0)
			cout<<"YES";
			else
			{
				c=y,d=p;
				flag=0;
				for(int i=1;i<=m;i++)
				{
					if(a[i]==c||b[i]==c||a[i]==d||b[i]==d)
					{
						continue;
					}
					else
					{
						flag=1;
						break;
					}
				}
				if(flag==0)
				cout<<"YES";
				else
				cout<<"NO";
			}
		}
	}
}