1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<vector>
 6 #include<map>
 7 using namespace std;
 8 #define pii pair<int,int>
 9 #define inf 0x3f3f3f3f
10 int f[50005],tot[50005];
11 map<int,int>M;
12 int getf(int v){return f[v]==v?v:f[v]=getf(f[v]);}
13 int main()
14 {
15     int a,b,i,j,k;
16     int N,cas=0;
17     while(cin>>a>>b){bool ok=1;N=0;
18     if(a<=-1&&b<=-1)break;
19     M.clear();
20     if(a==0&&b==0){printf("Case %d is a tree.\n",++cas);continue;}
21     M[a]=++N;
22     if(a!=b)M[b]=++N;
23     else M[b]=1;
24         memset(tot,0,sizeof(tot));
25         for(i=1;i<=50005;++i)f[i]=i;
26         tot[M[b]]++;
27         int fa=getf(M[a]),fb=getf(M[b]);
28         if(fa!=fb) f[fa]=fb;
29         while(cin>>a>>b){if(a==0&&b==0) break;
30             if(!M[a])M[a]=++N;
31             if(!M[b])M[b]=++N;
32             a=M[a];
33             b=M[b];
34 
35             fa=getf(a),fb=getf(b);
36             if(fa!=fb) f[fa]=fb;
37             N=max(N,max(a,b));
38             tot[b]++;
39         }
40         for(i=1;i<=N;++i)
41         {
42             if(tot[i]>1) {ok=0; break;}
43         }
44         int s=0;
45         for(i=1;i<=N;++i)
46         {
47             if(i==getf(i)) s++;
48             if(s>1){ok=0;break;}
49         }
50         ok?printf("Case %d is a tree.\n",++cas):printf("Case %d is not a tree.\n",++cas);
51     }
52     return 0;
53 }