def min_lightbulbs(M, R, street_lights):
    required_bulbs = 0
    position = 0
    index = 0

    while position < M:
        next_position = position
        while index < len(street_lights) and street_lights[index] - R <= position:
            next_position = max(next_position, street_lights[index] + R)
            index += 1

        if next_position == position:
            return "IMPOSSIBLE"

        position = next_position
        required_bulbs += 1

    return required_bulbs


def main():
    T = int(input())
    for t in range(1, T + 1):
        M, R, N = map(int, input().split())
        street_lights = list(map(int, input().split()))
        result = min_lightbulbs(M, R, street_lights)
        print(f"Case #{t}: {result}")


if __name__ == "__main__":
    main()