#include <bits/stdc++.h>
using namespace std;
const int N=100000+5;
int dfn[N],low[N],team[N],num[N],in[N],out[N];
bool instack[N];
int n,T,m,index,team_num;
vector<int> mp[N];
stack<int> S;
void Tarjan(int u)
{
    low[u]=dfn[u]=++index;
    S.push(u);
    instack[u]=1;
    for(int i=0;i<mp[u].size();i++)
    {
        int v=mp[u][i];
        if (!dfn[v])
        {
            Tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        else if (instack[v]) low[u]=min(low[u],dfn[v]);
    }
    if (dfn[u]==low[u])
    {
        team_num++;
        while(1)
        {
            int v=S.top(); S.pop();
            instack[v]=0;
            team[v]=team_num;  // v点是第几组
            num[team_num]++;  //第i组的点个数
            if (v==u) break;
        }
    }
}
void dfs()
{
  memset(low,0,sizeof(low));
  memset(dfn,0,sizeof(dfn));
  memset(instack,0,sizeof(instack));
  memset(team,0,sizeof(team));
  memset(num,0,sizeof(num));
  team_num=0;
  index=0;
  for(int i=1;i<=n;i++)
    if (!dfn[i]) Tarjan(i);
}
int main()
{
    scanf("%d",&T);
    for(int cas=1;cas<=T;cas++)
    {
        scanf("%d%d",&n,&m);
        for(int i=1;i<=n;i++) mp[i].clear();
        for(int i=1;i<=m;i++)
        {
            int x,y;
            scanf("%d%d",&x,&y);
            mp[x].push_back(y);
        }
        dfs();  //缩点，求出各个组的点数
        printf("Case %d: ",cas);
        for(int i=1;i<=team_num;i++) in[i]=out[i]=0;
        for(int i=1;i<=n;i++)
            for(int j=0;j<mp[i].size();j++)
        {
            if (team[i]!=team[mp[i][j]])
            {
                in[team[mp[i][j]]]++;
                out[team[i]]++;
            }
        }
        //统计入度数和出度数
        int minn=100000;
        for(int i=1;i<=team_num;i++)
            if (in[i]==0 || out[i]==0) minn=min(minn,num[i]);
        //求出入度=0或者出度=0的点数最小的组
        if (team_num==1) printf("-1\n");
            else printf("%lld\n",(long long)n*n-n-(long long)minn*(n-minn)-m);
    }
    return 0;
}