#include<stdio.h>
#include<string.h>
#include<iostream>
using namespace std;

const int MAXN = 100000+100;
/*
 * Tarjan算法
 * 复杂度O(N+M)
 */
struct Edge{
    int to,next;
}edge[MAXN];
int head[MAXN],tot;
int Low[MAXN],DFN[MAXN],Stack[MAXN],Belong[MAXN];//Belong数组的值是1~scc
int Index,top;
int scc;//强连通分量的个数
bool Instack[MAXN];
int num[MAXN];//各个强连通分量包含点的个数，数组编号1~scc

void init()
{
    tot=0;
    memset(head,-1,sizeof(head));
}

void addedge(int u,int v)
{
    edge[tot].to=v;
    edge[tot].next=head[u];
    head[u]=tot++;
}

void Tarjan(int u)
{
    int v;
    Low[u]=DFN[u]=++Index;
    Stack[top++]=u;
    Instack[u]=true;
    for(int i=head[u];i!=-1;i=edge[i].next){
        v=edge[i].to;
        if(!DFN[v]){
            Tarjan(v);
            if(Low[u]>Low[v]) Low[u]=Low[v];
        }
        else if(Instack[v]&&Low[u]>DFN[v])
            Low[u]=DFN[v];
    }
    if(Low[u]==DFN[u]){
        scc++;
        do{
            v=Stack[--top];
            Instack[v]=false;
            Belong[v]=scc;
            num[scc]++;
        }
        while(v!=u);
    }
}

void solve(int n)
{
    memset(DFN,0,sizeof(DFN));
    memset(Instack,false,sizeof(Instack));
    memset(num,0,sizeof(num));
    Index=top=scc=0;
    for(int i=1;i<=n;i++)
        if(!DFN[i])
           Tarjan(i);
}

int in[MAXN],out[MAXN];

int main()
{
    int T;
    int iCase=0;
    scanf("%d",&T);
    while(T--){
        iCase++;
        init();
        int n,m;
        scanf("%d%d",&n,&m);
        for(int i=1;i<=m;i++){
            int u,v;
            scanf("%d%d",&u,&v);
            addedge(u,v);
        }
        solve(n);
        if(scc==1){
            printf("Case %d: -1\n",iCase);
            continue;
        }
        for(int i=1;i<=scc;i++){
            in[i]=0;
            out[i]=0;
        }
        for(int u=1;u<=n;u++){
            for(int i=head[u];i!=-1;i=edge[i].next){
                int v=edge[i].to;
                if(Belong[u]==Belong[v]) continue;
                out[Belong[u]]++;
                in[Belong[v]]++;
            }
        }
        long long sss=(long long)n*(n-1)-m;
        long long ans=0;
        for(int i=1;i<=scc;i++){
            if(in[i]==0||out[i]==0)
                ans=max(ans,sss-(long long)num[i]*(n-num[i]));
        }
        printf("Case %d: %lld\n",iCase,ans);
    }
}