import sys
from collections import deque, Counter
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
inf = 2 ** 63 - 1
mod = 998244353
import string

def solve(test):
    n, r, m = mi()
    a = [v - r for v in li()][::-1]
    now = 0
    p = -inf
    ans = 0
    while a and now < n:
        while a and a[-1] <= now:
            p = a.pop()
        ans += 1
        now = p + 2 * r
        if ans > m:
            break
    if now < n:
        ans = "IMPOSSIBLE"
    print('Case #' + str(test) + ':', ans)
        




for test in range(1, ii() + 1):
    solve(test)