#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";
    }
}