import sys

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

MOD = 10**9 + 7

N, B, *S = map(int, read().split())

counter = [0] * N
for x in S:
    counter[x] += 1

powB = [1] * N
for n in range(1, N):
    powB[n] = powB[n - 1] * B % MOD

used = 0
f = 1
df = 0
for n in counter[::-1]:
    if not n:
        continue
    total = 1
    stay = 1
    for i in range(1, n + 1):
        total *= used + i
        stay *= used + i - 1
        total %= MOD
        stay %= MOD
    a = stay
    b = total - stay
    # a + bx をかける
    g = a + b * B
    dg = b
    f, df = f * g, f * dg + df * g
    f %= MOD
    df %= MOD
    used += n

print(df * B % MOD)