#include<iostream>

 #include<cstdio>

 #include<cstring>

 #include<iostream>

 #include<cstdio>

 #include<cstring>

 #include<cstdlib>

 #include<cmath>

 #include<climits>

 #include<algorithm>

 #include<stack>

 #include<map>

 #include<set>

 #include<vector>

 #include<queue>

 #include<list>

 using namespace std;

 #define MAXN 11111

 #define inf 1<<30

 #define INF 1LL<<60

 #define FILL(a,b) memset(a,b,sizeof(a))

 typedef long long ll;

 typedef unsigned long long llu;

 typedef pair<int,int>PP;

 template<class T> inline T Get_MIN(const T &a,const T &b){ return a < b ? a : b; }

 template<class T> inline T Get_MAX(const T &a,const T &b){ return a > b ? a : b; }

 template<class T> inline T ABS(const T &a){ return a <  ? -a : a; }

 struct Edge{

     int v,next;

 }edge[MAXN*];

 int n,m,NE;

 int head[MAXN];

 void Insert(int u,int v)

 {

     edge[NE].v=v;

     edge[NE].next=head[u];

     head[u]=NE++;

 }

 int low[MAXN],dfn[MAXN],color[MAXN];

 bool mark[MAXN];

 int scc_count,cnt;

 stack<int>S;

 void Tarjan(int u)

 {

     low[u]=dfn[u]=++cnt;

     mark[u]=true;

     S.push(u);

     for(int i=head[u];i!=-;i=edge[i].next){

         int v=edge[i].v;

         if(dfn[v]==){

             Tarjan(v);

             low[u]=Get_MIN(low[u],low[v]);

         }else if(mark[v]){

             low[u]=Get_MIN(low[u],dfn[v]);

         }

     }

     if(low[u]==dfn[u]){

         scc_count++;

         int v;

         do{

             v=S.top();

             S.pop();

             mark[v]=false;

             color[v]=scc_count;

         }while(u!=v);

     }

 }

 int degree[MAXN];

 int main()

 {

     int _case,u,v,ans,t=;

     scanf("%d",&_case);

     while(_case--){

         scanf("%d%d",&n,&m);

         NE=;

         FILL(head,-);

         FILL(dfn,);

         FILL(mark,false);

         cnt=scc_count=;

         while(m--){

             scanf("%d%d",&u,&v);

             Insert(u,v);

         }

         for(int i=;i<=n;i++)if(dfn[i]==)Tarjan(i);

         FILL(degree,);

         for(int u=;u<=n;u++){

             for(int i=head[u];i!=-;i=edge[i].next){

                 int v=edge[i].v;

                 if(color[u]!=color[v]){

                     degree[color[v]]++;

                 }

             }

         }

         ans=;

         for(int i=;i<=scc_count;i++)if(degree[i]==)ans++;

         printf("Case %d: %d\n",t++,ans);

     }

     return ;

 }