T = int(input())

for case in range(1, T+1):
    M, R, N = map(int, input().split())
    X = list(map(int, input().split()))

    # Initialize pointers
    l = r = 0
    ans = 0

    while r < N:
        # Find the rightmost street light that is covered
        while r < N and X[r] - X[l] <= R:
            r += 1

        # If we covered all street lights, we are done
        if r == N:
            ans += 1
            break

        # Find the leftmost uncovered street light outside the coverage range
        while l < r and X[r] - X[l] > R:
            l += 1

        # If there is no uncovered street light within the coverage range, it is impossible
        if l == r:
            ans = "IMPOSSIBLE"
            break

        # Cover the segment of freeway from X[l] to X[r-1] with a new lightbulb
        ans += 1

    print("Case #{}: {}".format(case, ans))