from sys import stdin
from collections import deque
GI = lambda: int(input())
gi = lambda: list(map(int, input().split()))
T = GI()
def solve(id):
    M, R, N = gi()
    arr = gi()
    cur = pt = cnt = 0
    while cur < M:
        best = -1
        while pt < len(arr) and arr[pt] - R <= cur:
            best = pt
            pt += 1
        if best == -1: return "IMPOSSIBLE"
        cnt += 1
        cur = arr[best] + R
    return str(cnt)
for i in range(1, T + 1):
    print("Case #%d: %s" % (i, solve(i)))
exit(0)