#include<cstdio>

#include<cmath>

#include<cstring>

#include<algorithm>

using namespace std;

const int N=;

int an[N],ans,a[N][N],n,x;

void dfs(int x,int y)

{

    if (ans)return;

    an[x]=y;

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

     if ((!a[x][i]||!a[i][x])&&i!=x)

      {

          if (an[i]&&-y!=an[i]){ans=;return;}

          if (!an[i])dfs(i,-y);

      }

}

int main()

{

    while (~scanf("%d",&n))

     {

         ans=;

         memset(an,,sizeof an);

         memset(a,,sizeof a);

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

          for (scanf("%d",&x);x;scanf("%d",&x))a[i][x]=;

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

         if (!an[i])dfs(i,);

        if (ans)puts("NO");else puts("YES");

     }

}