import fileinput
import sys

sys.setrecursionlimit(10**6)

lines = fileinput.input()

def read(conv=str, sep=None):
    global lines
    line = lines.readline().strip()
    if sep is None:
        return conv(line)
    else:
        return [conv(token) for token in line.split(sep)]

def eprint(*args, **kwargs):
    print(*args, file=sys.stderr, **kwargs)

def encode(D, s):
    e = [None] * len(s)
    for i, c in enumerate(s):
        e[i] = D[ord(c) - ord('A')]
    return ''.join(e)

def solve(M, R, N, X):
    m = 0
    i = 0
    n = 0
    while m < M:
        if i == N:
            # we need more lights, but we have no more
            return None
        while i+1 < N and m + R >= X[i+1]:
            i += 1
        if m + R < X[i]:
            # we don't have light covering this space
            return None
        m = X[i] + R
        i += 1
        n += 1
    return n

T = read(int)
for t in range(T):
    M, R, N = read(int, ' ')
    X = read(int, ' ')
    sol = solve(M, R, N, X)
    print("Case #{0}: {1}".format(t + 1, "IMPOSSIBLE" if sol is None else sol))