N,K=(int(x) for x in input().split())
A=list(map(int, input().split()))
A=sorted(A)
mod=998244353
bunbo=1
num=0
for i in A:
    if i >= K:
        bunbo *= i
        bunbo %= mod
        num += 1

bunshi = K**(num) - (K-1)**(num)
bunshi = pow(K,num,mod) - pow(K-1,num,mod)
if bunshi < 0:
    bunshi += mod

def extended_gcd(a, b):
    if b == 0:
        return a, 1, 0
    g, x, y = extended_gcd(b, a % b)
    return g, y, x - (a // b) * y

def solve(N, S, K):
    a = K
    b = N
    c = (-S) % N

    g, x, y = extended_gcd(a, b)

    if c % g != 0:
        return -1

    x0 = (x * (c // g)) % (N // g)
    return x0

ans = solve(mod, bunshi, -bunbo)
print(ans)