#include <cstdio>

 #include <cstring>

 #include <cmath>

 #include <queue>

 #include <algorithm>

 using namespace std;

 int flag[];

 int p[][];

 int o[][];

 int n,z;

 void dfs(int x,int step)

 {

     int i;

     if(z) return ;

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

     {

         if(i == x) continue;

         if(o[x][i]&&!flag[i])

         {

             flag[i] = step% + ;

             dfs(i,step+);

         }

         else if(o[x][i]&&flag[i])

         {

             if(flag[i] != step% + )

             {

                 z = ;

                 return ;

             }

         }

     }

     return ;

 }

 int main()

 {

     int i,j;

     while(scanf("%d",&n)!=EOF)

     {

         memset(flag,,sizeof(flag));

         memset(p,,sizeof(p));

         memset(o,,sizeof(o));

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

         {

             for(;;)

             {

                 scanf("%d",&j);

                 if(j == ) break;

                 p[i][j] = ;

             }

         }

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

         {

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

             {

                 if(!p[i][j]||!p[j][i])

                 o[i][j] = o[j][i] = ;

             }

         }

         z = ;

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

         {

             if(!flag[i])

             {

                 flag[i] = ;

                 dfs(i,);

             }

         }

         if(z)

             printf("NO\n");

         else

             printf("YES\n");

     }

     return ;

 }