#!/usr/bin/env python3

def solve(m, rad, n, x):
    if n == 0:
        return -1
    distances = []
    for bulb in x:
        distances.append([max(0, bulb - rad), min(m, bulb + rad)])
    if distances[0][0] > 0:
        return -1
    if distances[-1][1] < m:
        return -1

    l = 0
    bulbs = []
    for i in range(n):
        if distances[i][0] > l:
            bulbs.append(i - 1)
            l = distances[i-1][1]
            if distances[i][0] > l:
                return -1
    if len(bulbs) == 0:
        return 1

    if distances[bulbs[-1]][1] < m:
        bulbs.append(1)

    return len(bulbs)


def main():
    t = int(input())
    for tc in range(1, t+1):
        m, r, n = map(int, input().split())
        x = list(map(int, input().split()))
        res = solve(m, r, n, x)
        res = res if res != -1 else "IMPOSSIBLE"
        print(f"Case #{tc}: {res}")


if __name__ == "__main__":
    main()