tjut 4635

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>

using namespace std;

const int VM=200010;
const int EM=200010;
const int INF=0x3f3f3f3f;

struct Edge{
int to,nxt;
}edge[EM<<1];

long long n,m,cnt,head[VM];
long long dep,top,atype;
long long dfn[VM],low[VM],vis[VM],stack[VM],belong[VM],indeg[VM],outdeg[VM],sum[VM];

void addedge(int cu,int cv){
edge[cnt].to=cv;    edge[cnt].nxt=head[cu];     head[cu]=cnt++;
}

void Tarjan(int u){
dfn[u]=low[u]=++dep;
stack[top++]=u;
vis[u]=1;
for(int i=head[u];i!=-1;i=edge[i].nxt){
int v=edge[i].to;
if(!dfn[v]){
Tarjan(v);
low[u]=min(low[u],low[v]);
}else if(vis[v]){
low[u]=min(low[u],dfn[v]);
}
}
int j;
if(dfn[u]==low[u]){
atype++;
do{
j=stack[--top];
belong[j]=atype;
sum[atype]++;   //记录每个连通分量中点的个数
//printf("            sum[%lld]=%lld\n",atype,sum[atype]);
vis[j]=0;
}while(u!=j);
}
}

void init(){
cnt=0;
memset(head,-1,sizeof(head));
dep=0,  top=0,  atype=0;
memset(dfn,0,sizeof(dfn));
memset(low,0,sizeof(low));
memset(vis,0,sizeof(vis));
memset(belong,0,sizeof(belong));
memset(indeg,0,sizeof(indeg));
memset(outdeg,0,sizeof(outdeg));
memset(sum,0,sizeof(sum));
}

int main(){

//freopen("input.txt","r",stdin);

int t,cases=0;
scanf("%d",&t);
while(t--){
cin>>n>>m;
if(n==1){
printf("Case %d: -1\n",++cases);
continue;
}
init();
int u,v;
for(int i=0;i<m;i++){
scanf("%d%d",&u,&v);
addedge(u,v);
}
for(int i=1;i<=n;i++)
if(!dfn[i])
Tarjan(i);
if(atype==1){
printf("Case %d: -1\n",++cases);
continue;
}
for(int u=1;u<=n;u++)
for(int i=head[u];i!=-1;i=edge[i].nxt){
int v=edge[i].to;
if(belong[u]!=belong[v]){
outdeg[belong[u]]++;
indeg[belong[v]]++;
}
}
long long ans=0,tmp;
for(long long i=1;i<=atype;i++)
if(indeg[i]==0 || outdeg[i]==0){    //找出度或者入度为0的点，包含节点数最少的那个点
//令它为一个部，其它所有点加起来做另一个部，就可以得到最多边数的图了
tmp=sum[i];
ans=max(ans,tmp*(tmp-1)+(n-tmp)*(n-tmp-1)+tmp*(n-tmp)-m);
}
cout<<"Case "<<(++cases)<<": "<<ans<<endl;
}
return 0;
}