from __future__ import division, print_function

import array
import bisect
import collections
import decimal
import fractions
import functools
import heapq
import itertools
import math
import random
import re
import sys

try:
    input = raw_input
except NameError:
    pass

# decimal.getcontext().prec = 50
# sys.setrecursionlimit(1000000)
# MOD = 10**9 + 7
# INF = float('inf')
IMPOSSIBLE = "IMPOSSIBLE"
POSSIBLE = "POSSIBLE"


def gcd(a, b):
    """greatest common divisor"""
    if b == 0:
        return a
    else:
        return gcd(b, a % b)


def egcd(a, b):
    """return (g, x, y), a*x + b*y = gcd(x, y)"""
    if a == 0:
        return (b, 0, 1)
    else:
        g, y, x = egcd(b % a, a)
        return (g, x - (b // a) * y, y)


def solve(f):
    w, n, d = f.read_int_list()
    x = f.read_int_list()

    ans = 0
    for i in range(w // 2):
        diff = x[i] - x[w - i - 1]
        if diff == 0:
            continue
        g, a, b = egcd(d, -n)
        base = diff // g
        # print(f"{a}*{d} - {b}*{n} = {g}")
        if diff % g != 0:
            return IMPOSSIBLE
        # print(f"{a*base}*{d} - {b*base}*{n} = {g*base}")
        m0 = a * base
        cnt = m0 % (n // g)
        # print(g, a, b, diff, m0, cnt)
        ans += min(cnt, abs(cnt - n // g))

    return ans


class Reader(object):
    def __init__(self, filename=None):
        self.file = open(filename) if filename is not None else None
        self.case = 1

    def __readline(self):
        return next(self.file).strip() if self.file else input()

    def next_case(self):
        next(self.file)
        self.case += 1

    def read_int(self):
        return int(self.__readline())

    def read_float(self):
        return float(self.__readline())

    def read_decimal(self):
        return decimal.Decimal(self.__readline())

    def read_str(self):
        return self.__readline()

    def read_int_list(self):
        return list(map(int, self.__readline().split()))

    def read_float_list(self):
        return list(map(float, self.__readline().split()))

    def read_decimal_list(self):
        return list(map(decimal.Decimal, self.__readline().split()))

    def read_str_list(self):
        return self.__readline().split()


if __name__ == "__main__":
    filename = sys.argv[1] if len(sys.argv) > 1 else None
    f = Reader(filename)
    cases = f.read_int()
    for case in range(cases):
        line = "Case #%d: %s\n" % (case + 1, str(solve(f)))
        print(line, end="")