alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
t = int(input())
for u in range(t):
    [m,r,n] = [int(i) for i in input().split()]
    x = [int(i) for i in input().split()]
    x.reverse()
    last = 0
    nextlamp = x.pop()
    ans = 0
    while last < m:
        if nextlamp - last > r:
            ans = 'IMPOSSIBLE'
            break
        if len(x) == 0:
            ans += 1
            last = nextlamp + r
            nextlamp = m + r + 1
        else:
            nextnext = x.pop()
            if nextnext - last <= r:
                nextlamp = nextnext
            else:
                ans += 1
                last = nextlamp + r
                nextlamp = nextnext
    print('Case #' + str(u+1) + ':', ans)