1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <vector>
 5 using namespace std;
 6 
 7 const int maxn = 105;
 8 int G[maxn][maxn];
 9 vector<int> mat[maxn];
10 int color[maxn];
11 
12 bool is_bi(int u) {
13     for(int i = 0; i < mat[u].size(); i++) {
14         int v = mat[u][i];
15         if(color[v] == color[u]) return false;
16         if(color[v] == 0) {
17             color[v] = 3 - color[u];
18             if(!is_bi(v)) return false;
19         }
20     }
21     return true;
22 }
23 
24 bool solve(int n) {
25     for(int i = 1; i <= n; i++) {
26         memset(color, 0, sizeof(color));
27         color[i] = 1;
28         if(!is_bi(i)) return false;
29     }
30     return true;
31 }
32 
33 int main() {
34     int n;
35     int id;
36     while(EOF != scanf("%d",&n)) {
37         memset(G, 0, sizeof(G));
38         memset(mat, 0, sizeof(mat));
39         for(int i = 1; i <= n; i++) {
40             mat[i].clear();
41             while(scanf("%d",&id) && id) {
42                 G[i][id] = 1; 
43             }
44         }
45         for(int i = 1; i <= n; i++) {
46             for(int j = 1; j <= n; j++) {
47                 if(i == j) continue;
48                 if(G[i][j] + G[j][i] != 2) {
49 //                    printf("%d %d\n",i, j);
50                     mat[i].push_back(j);
51                     mat[j].push_back(i);
52                 }
53             }
54         }
55         if(solve(n)) puts("YES");
56         else puts("NO");
57     }
58     return 0;
59 }