/*

     水题：判断前后的差值是否为1，b[i]记录差值，若没有找到，则是第一个出错

 */

 #include <cstdio>

 #include <iostream>

 #include <algorithm>

 #include <cstring>

 #include <string>

 #include <cmath>

 using namespace std;

 const int MAXN = 1e5 + ;

 const int INF = 0x3f3f3f3f;

 int a[MAXN];

 int b[MAXN];

 int main(void)        //HDOJ 4727 The Number Off of FFF

 {

     //freopen ("L.in", "r", stdin);

     int t, cas = ;

     int n;

     scanf ("%d", &t);

     while (t--)

     {

         scanf ("%d", &n);

         a[] = b[] = ;

         for (int i=; i<=n; ++i)

         {

             scanf ("%d", &a[i]);

             b[i] = a[i] - a[i-];

         }

         int ans = -;

         for (int i=; i<=n; ++i)

         {

             if (b[i] != )

             {

                 ans = i;    break;

             }

         }

         if (ans == -)    ans = ;

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

     }

     return ;

 }

 /*

 Case #1: 3

 Case #2: 3

 */