#include<stdio.h>
#include<string.h>
#include<algorithm>using namespace std;const int maxn = 100005;
const int maxm = 100005;
int n, m;
int top, tol, cnt;
int stacksize;struct Node{int u;int v;int next;
};
Node node[maxm];
int dfn[maxn];
int low[maxn];
int vis[maxn];
int num[maxn];
int indi[maxn];
int oudi[maxn];
int head[maxn];
int stack[maxn];
int point[maxn];void init() {tol = top = stacksize = cnt = 0;memset(dfn, 0, sizeof(dfn));memset(low, 0, sizeof(low));memset(num, 0, sizeof(num));memset(indi, 0, sizeof(indi));memset(oudi, 0, sizeof(oudi)); memset(node, 0, sizeof(node));memset(head, -1, sizeof(head));memset(vis, false, sizeof(vis));memset(point, 0, sizeof(point));memset(stack, 0, sizeof(stack));
}void addnode(int u, int v) {node[tol].u = u;node[tol].v = v;node[tol].next = head[u];head[u] = tol++;
}void dfs(int u) {int v;dfn[u] = low[u] = ++cnt;stack[stacksize++] = u;vis[u] = true;for(int i=head[u]; i!=-1; i=node[i].next) {v = node[i].v;if(!dfn[v]) {dfs(v);low[u] = min(low[u], low[v]);} else if(vis[v]) {low[u] = min(low[u], dfn[v]);}}if(low[u] == dfn[u]) {top++;do{v = stack[--stacksize];vis[v] = false;num[top]++;point[v] = top;} while(v != u);}
}void tarjan() {for(int i=1; i<=n; i++) {if(!dfn[i]) {dfs(i);}}
}int solve() {for(int u=1; u<=n; u++) {for(int i=head[u]; i+1; i=node[i].next) {int v = node[i].v;if(point[u] != point[v]) {oudi[point[u]]++;indi[point[v]]++;}}}int ans = 0;for(int i=1; i<=top; i++) {if(!oudi[i] || !indi[i]) {ans = max(ans, n*n-n-m-(n-num[i])*num[i]);}}return ans;
}int main() {int T;scanf("%d", &T);int cas = 1;while(T--) {init();scanf("%d%d", &n, &m);for(int i=0; i<m; i++) {int u, v;scanf("%d%d", &u, &v);addnode(u, v);}tarjan();if(top == 1) {printf("Case %d: -1\n", cas++);} else {int ans = solve();printf("Case %d: %d\n", cas++, ans);}}
}