def install_lightbulbs(M, R, N, street_lights):
    street_lights.sort()
    num_lightbulbs = 0
    i = 0

    while i < N:
        # Find the furthest street light that can be illuminated by a single lightbulb
        furthest_light = -1
        while i < N and street_lights[i] <= furthest_light + R:
            i += 1
        if i == N:
            break

        # If there is a gap between the last street light and the furthest light that can be illuminated,
        # it's impossible to cover the entire freeway
        if street_lights[i-1] + R < M:
            return "IMPOSSIBLE"

        num_lightbulbs += 1
        furthest_light = street_lights[i-1] + R

    return num_lightbulbs


# Read input
Tc = int(input())  # Number of test cases
for t in range(1, Tc+1):
    M, R, N = map(int, input().split())  # Read freeway length, lightbulb illumination radius, and number of street lights
    street_lights = list(map(int, input().split()))  # Read the positions of street lights
    result = install_lightbulbs(M, R, N, street_lights)
    print("Case #{}: {}".format(t, result))