from sys import stdin
input = stdin.readline

def solve(m,r,n,polls):
    polls.sort()

    ranges = []

    for i in range(n):
        left = max(0, polls[i] - r)
        right = min(m, polls[i] + r)
        ranges.append((left,right))

    # print(ranges)

    covered = 0

    count = 0
    included = None

    i = 0
    while i < n:
        l,r = ranges[i]
        
        if l > covered:
            if i==0:
                return 'IMPOSSIBLE'
            if included == i-1:
                return 'IMPOSSIBLE'
            
            covered = ranges[i-1][1]
            included = i-1
            count+=1
            continue

        i+=1


    if covered < m:
        if included == n-1:
            return 'IMPOSSIBLE'
        
        if ranges[n-1][0] > covered:
            return 'IMPOSSIBLE'
        
        if ranges[n-1][1] < m:
            return 'IMPOSSIBLE'
        
        count+=1


    return count




    

for i in range(int(input())):
    m,r,n = map(int, input().split())

    polls = list(map(int, input().split()))

    
    print(f'Case #{i+1}: {solve(m,r,n,polls)}')