/*   @JUDGE_ID:   1705PZ   615   C */
#include <stdio.h>

int main()
{
	int i,m,n,count,t = 1,flag;
	int table[1000][2];

	while(1)
	{
		count = 0;
		scanf("%d %d",&m,&n);
		if(m == 0 && n == 0)
		{
			printf("Case %d is a tree.\n",t++);
			continue;
		}
		if(m < 0 && n < 0)
			break;

		flag = 1;
		for(i = 0;i < count;i++)
			if(m == table[i][0])
				flag = 0;
		if(flag)
		{
			table[count][0] = m;
			table[count++][1] = 0;
		}

		flag = 1;
		for(i = 0;i < count;i++)
			if(n == table[i][0])
			{
				flag = 0;
				table[i][1]++;
			}
		if(flag)
		{
			table[count][0] = n;
			table[count++][1] = 1;
		}

		while(1)
		{
			scanf("%d %d",&m,&n);
			if(m == 0 && n == 0)
				break;

			flag = 1;
			for(i = 0;i < count;i++)
				if(m == table[i][0])
					flag = 0;
			if(flag)
			{
				table[count][0] = m;
				table[count++][1] = 0;
			}

			flag = 1;
			for(i = 0;i < count;i++)
				if(n == table[i][0])
				{
					flag = 0;
					table[i][1]++;
				}
			if(flag)
			{
				table[count][0] = n;
				table[count++][1] = 1;
			}
		}

		flag = 0;
		for(i = 0;i < count;i++)
			if(table[i][1] == 0)
				flag++;
		if(flag != 1)
		{
			printf("Case %d is not a tree.\n",t++);
			continue;
		}

		flag = 0;
		for(i = 0;i < count;i++)
			if(table[i][1] > 1)
			{
				printf("Case %d is not a tree.\n",t++);
				flag = 1;
				break;
			}
		if(flag)
			continue;

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

	return 0;
}
@END_OF_SOURCE_CODE