def solve_case(case_num, m, r, street_lights):
    street_lights.append(m + r + 1) # add an extra light to cover the end of the freeway
    n = len(street_lights)
    i, j = 0, 0 # i is the leftmost uncovered point, j is the rightmost covered point
    bulbs = 0
    
    while i < m:
        if street_lights[j] - r <= i:
            # the current light covers the current point
            j += 1
        elif j < n - 1 and street_lights[j+1] - r <= i:
            # the next light covers the current point
            j += 1
            bulbs += 1
        else:
            # no light covers the current point
            print(f"Case #{case_num}: IMPOSSIBLE")
            return
        
        if street_lights[j] + r < street_lights[j+1]:
            # need to add a new light to cover the gap
            i = street_lights[j] + r
            bulbs += 1
        else:
            i = street_lights[j] + r
    
    print(f"Case #{case_num}: {bulbs}")

# read input and process cases
T = int(input())
for case_num in range(1, T+1):
    M, R, N = map(int, input().split())
    street_lights = list(map(int, input().split()))
    solve_case(case_num, M, R, street_lights)