#include<iostream>
#include<cstdio>
#include<vector>
#include<cstdio>
#include<cstring>
#include<string>
#include<set>
#include<queue>
#include<map>
using namespace std;
#define max 100001
vector<long long>v[max];
void bfs();
long long check=0;
set<long long>v1;
void DFS();
void DFS_VISIT(long long u);
string color[max];
vector<long long>top_sort;
queue<long long>q;
int main()
{
long long k=0,i;
long long n,m;
map< long long,long long > city;
long long ind=0;
while(cin>>n>>m)
{
if(n<0&&m<0)
{
break;
}
if(city[n]==0)
{
city[n]=++ind;
}
if(city[m]==0)
{
city[m]=++ind;
}
if(n>0&&m>0)
{
v[city[n]].push_back(city[m]);
v1.insert(city[n]);
v1.insert(city[m]);
}
if(n==0&&m==0)
{
check=0;
if(v1.size()>0)
{
DFS();
bfs();
}
if(v1.size()==0)
printf("Case %lld is a tree.\n",++k);
else if(check==0)
printf("Case %lld is a tree.\n",++k);
else
printf("Case %lld is not a tree.\n",++k);
top_sort.clear();
set<long long>::iterator it;
for (it=v1.begin();it!=v1.end();it++)
{
v[*it].clear();
}
city.clear();
while(!q.empty())
q.pop();
v1.clear();
ind=0;
}
}
}
void DFS()
{
set<long long>::iterator it;
for (it=v1.begin();it!=v1.end();it++)
{
color[*it] = "WHITE";
}
set<long long>::iterator it1;
for (it1=v1.begin();it1!=v1.end();it1++)
{
if (color[*it1] == "WHITE")
{
DFS_VISIT(*it1);
}
}
}
void DFS_VISIT(long long u)
{
long long i;
color[u] = "GRAY";
for (i = 0; i<v[u].size(); i++)
{
if (color[v[u][i]] == "WHITE")
{
DFS_VISIT(v[u][i]);
}
}
color[u] = "BLACK";
top_sort.push_back(u);
}
void bfs()
{
int taken[max];
memset(taken,-1,sizeof(taken));
long long i,u2,v2,j;
for(i=top_sort.size()-1;i>=0;i--)
{
if(taken[top_sort[i]]!=1)
{
taken[top_sort[i]]=1;
q.push(top_sort[i]);
while(!q.empty())
{
u2=q.front();
q.pop();
for(j=0;j<v[u2].size();j++)
{
v2=v[u2][j];
if(taken[v2]==1)
{
check=1;
}
if(taken[v2]==-1)
{
taken[v2]=1;
q.push(v2);
}
}
}
}
}
}
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