1 #include<iostream>
 2 #include<cstdlib>
 3 #include<string.h>
 4 #include<stdio.h>
 5 #include<cstring>
 6 #include<algorithm>
 7 #include<climits>
 8 #include<math.h>
 9 #include<vector>
10 #include<cstdio>
11 using namespace std;
12 #define maxn 100005
13 int  visit[maxn];
14 int father[maxn];
15 int cic;
16 int ding;
17 int edge;
18 void init()
19 {
20     for(int i=1;i<=maxn;i++)
21         visit[i]=0,father[i]=i;
22     ding=0;edge=0;
23 }
24 int find(int x)
25 {
26     if(father[x]==x)return x;
27     else find(father[x]);
28 }
29 
30 void man(int a,int b)
31 {
32     int x,y;
33     x=find(a);
34     y=find(b);
35     if(x!=y)
36         father[x]=y;
37 }
38 int main()
39 {
40     int a,b,t=1,p;
41     while(1)
42     {
43         init();
44         p=0;
45         cin>>a>>b;
46         if(a==0&&b==0)
47             {cout<<"Case "<<t<<" is a tree."<<endl;continue;}
48         if(a<0&&b<0)break;
49         man(a,b);
50         visit[a]=1;
51         visit[b]=2;
52         edge++;
53         while(1)
54         {
55             cin>>a>>b;
56             if(a==0&&b==0)break;
57             visit[a]=1;
58             if(visit[b]==2)p=1;
59             else visit[b]=2;
60             edge++;
61             man(a,b);
62         }
63         for(int i=1;i<=maxn;i++)
64             if(visit[i]!=0)ding++;
65         if(ding-1==edge&&!p)cout<<"Case "<<t<<" is a tree."<<endl;
66         else cout<<"Case "<<t<<" is not a tree."<<endl;
67         t++;
68     }
69     return 0;
70 }