#include<vector>
#include<iostream>
using namespace std;
bool used[100113];
vector<int>gr[100113];
int pr[100113];
bool x = false;
int k;
bool dfs(int v, int p)
{
	bool fl = false;
	used[v] = 1; pr[v] = p;
	for (int i = 0; i < gr[v].size(); i++)
	{
		if (v == k)
		{
			return true;
		}
		if ((!used[gr[v][i]]))
		{
			fl = dfs(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);
	}
	bool z1 = dfs(1, 0);
	used[0] = 0;
	bool z2 = dfs(1, 0);
	if (z1 && z2)
	{
		cout << "YES";
	}
	else
	{
		cout << "NO";
	}
}