#define _CRT_SECURE_NO_WARNINGS
#include<vector>
#include<iostream>
using namespace std;
bool used[100113];
bool desu[100113];
vector<int>gr[100113];
int pr[100113];
bool x = false;
int k;
int m = 0;
bool dfs2(int v, int p)
{
	bool fl = false;
	used[v] = 1; pr[v] = p;
	if (m == 0)
	{
		desu[v] = 1;
	}
	if (v == k)
	{
		m++;
	}
	for (int i = 0; i < gr[v].size(); i++)
	{
		if ((gr[v][i] != p) && (desu[gr[v][i]]))
		{
			return true;
		}
		if ((!used[gr[v][i]]))
		{
			fl=dfs2(gr[v][i], v);
		}
	}
	return fl;

}
int main()
{
	int a, b;
	cin >> a >> b >> k;
	int h1, h2;
	for (int i = 0; i < b; i++)
	{
		cin >> h1 >> h2;
		gr[h1].push_back(h2);
		gr[h2].push_back(h1);
	}
	if (b == 1)
	{
		cout << "NO";
		return 0;
	}
	int z=dfs2(1, 0);
	if (z)
	{
		cout << "YES";
	}
	else
	{
		cout << "NO";
	}
}