import sys
input = sys.stdin.readline
from collections import deque
from bisect import bisect_left, bisect_right
import itertools
#from math import *

for t in range(1, int(input())+1):

    m, r, n = map(int, input().split())
    arr = list(map(int, input().split()))
    ans = 0
    c = 0
    pind = -1
    ans = 0
    while c < m:
        tg = c+r
        ind = bisect_right(arr, tg)
        ind -= 1
        if ind == pind:
            ans = "IMPOSSIBLE"
            break
        pind = ind
        ans += 1
        c = arr[ind]+r
    print("Case #{}: {}".format(t, ans))