## https://yukicoder.me/problems/no/3166


def solve2(N, L, K, X, p):
    if 2 * p >= L:
        return True

    # 座標圧縮
    x_set = {0, L, 2 * L}
    for x in X:
        p1 = x - p
        p2 = x + p
        x_set.add(p1)
        x_set.add(x)
        x_set.add(p2)
        x_set.add(p1 + L)
        x_set.add(x + L)
        x_set.add(p2 + L)
        x_set.add(p1 + 2 * L)
        x_set.add(x + 2 * L)
        x_set.add(p2 + 2 * L)

    x_list = list(x_set)
    x_list.sort()
    x_map = {}
    for i, x in enumerate(x_list):
        x_map[x] = i
    x_len = len(x_list)

    # 円周を加味したimos法
    array = [0] * (3 * x_len  + 1)
    for x in X:
        p1 = x - p
        p2 = x + p
        for j in (L, 2 * L):
            y1 = x_map[(p1 + j)]
            y2 = x_map[(p2 + j)]
            array[y1] += 1
            array[y2] -= 1
    
    z = 0
    for i in range(3 * x_len + 1):
        z += array[i]
        array[i] = z
    j0 = x_map[L]
    j1 = x_map[2 * L]
    for j in range(j0, j1):
        if array[j] < K:
            return False
    return True



def solve(N, L, K, X):
    x_list = [2 * x for x in X]
    low = 0
    high = 2 * L
    while high - low > 1:
        mid = (high + low) // 2
        if solve2(N, 2 * L, K, x_list, mid):
            high = mid
        else:
            low = mid

    if solve2(N, 2 * L, K, x_list, low):
        p = low
    else:
        p = high
    if p % 2 == 1:
        return (p // 2) + 1
    else:
        return p // 2

    







def main():
    T = int(input())
    answers = []
    for _ in range(T):
        N, L, K = map(int, input().split())
        X = list(map(int, input().split()))
        ans = solve(N, L, K, X)
        answers.append(ans)

    for ans in answers:
        print(ans)




        





    



if __name__ == "__main__":
    main()