import bisect

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

    ans = 0
    frontier = 0
    while frontier < M:
        i = bisect.bisect(Xs, frontier + R)
        new_frontier = Xs[i-1] + R
        if i == 0 or frontier == new_frontier:
            ans = "IMPOSSIBLE"
            break
        ans += 1
        frontier = new_frontier
    print(f"Case #{case}: {ans}")