1 #include<stdio.h>

 2 #include<string.h>

 3 #include<iostream>

 4 #include<algorithm>

 5 #include<queue>

 6 #include<map>

 7 #include<vector>

 8 #include<math.h>

 9 #define mem(a,x) memset(a,x,sizeof(a))

10 using namespace std;

11 typedef long long ll;

12 const int maxn=120000+10;

13 const int mod=26;

14 const int INF=0x3f3f3f3f;

15 const int Times = 10;

16 const int N = 5500;

17 int v[maxn],vis[maxn],sum[maxn];

18 int flag=0;

19 int finds(int x)

20 {

21     if(x!=v[x])

22     {

23         int y=finds(v[x]);

24         return v[x]=y;

25     }

26     return x;

27 }

28 void join(int a,int b)

29 {

30     int fa=finds(a),fb=finds(b);

31     if(fa!=fb)

32         v[fa]=fb;

33     else

34         flag=1;

35 }

36 int main()

37 {

38     int a,b,p=1,edge;

39     while(scanf("%d%d",&a,&b))

40     {

41         flag=0;

42         edge=0;

43         for(int i=1; i<maxn; i++)

44         {

45             v[i]=i;

46         }

47         memset(vis,0,sizeof(vis));

48         memset(sum,0,sizeof(sum));

49         if(a<0&&b<0)

50             break;

51         if(a==0&&b==0)

52         {

53             printf("Case %d is a tree.\n",p);

54             p++;

55             continue;

56         }

57         vis[a]=vis[b]=1;

58         join(a,b);

59         sum[b]++;

60         edge++;

61         while(scanf("%d%d",&a,&b))

62         {

63             if(a==0&&b==0)

64                 break;

65             join(a,b);

66             vis[a]=vis[b]=1;

67             sum[b]++;

68             edge++;

69         }

70         if(flag==1)

71         {

72             printf("Case %d is not a tree.\n",p++);

73         }

74         else

75         {

76             int flagg=0,node=0;

77             for(int i=1; i<maxn; i++)

78             {

79                 if(vis[i]==1)

80                     node++;

81                 if(sum[i]>1)

82                     flagg=1;

83             }

84             if(node==(edge+1)&&flagg==0)

85             {

86                 printf("Case %d is a tree.\n",p++);

87             }

88             else

89             {

90                 printf("Case %d is not a tree.\n",p++);

91             }

92         }

93     }

94 }