def solution():
    M, R, N = list(map(int, input().strip().split()))
    X = list(map(int, input().strip().split()))
    X.sort()
    result = curr = 0
    for i in range(N+1):
        if i < N and X[i]-R <= curr:
            continue 
        if not (i-1 >= 0 and X[i-1]-R <= curr):
            break
        curr = X[i-1]+R
        result += 1
        if curr >= M:
            break
    return result if curr >= M else "IMPOSSIBLE"

for case in range(int(input())):
    print('Case #%d: %s' % (case+1, solution()))