#include<iostream>

#include<string>

#include<cstring>

using namespace std;//dfs

int flag;

int p[];

int a[][];

void Dfs(int n,int m)//起点,终点

{

    if (n == m)

    {

        flag = ;

        return;

    }

    for (int i = ; i < ; i++)

    {

        if (a[n][i] && !p[a[n][i]])

        {

            p[a[n][i]] = ;

            Dfs(a[n][i], m);

            p[a[n][i]] = ;//???

        }

    }

}

int main()

{

    int n;

    int m;

    while (cin >> n && n != )

    {

        flag = ;

        for (int i = ; i <=n;i++)

        {

            for (int j = ; j < ; j++)

            {

                cin >> a[i][j];

            }

        }

        cin >> m;//代表终点

        p[] = ;//起点访问过

        Dfs(,m);

        if (flag == )

            cout << "YES" << endl;

        else

            cout << "NO" << endl;

    }

    return ;

}