#include <iostream>
#include <vector>
#include <algorithm>
#include <cassert>
using ll = long long;
constexpr ll MOD = 1000000007;
template <typename T>
constexpr std::pair<T, T> extgcd(const T a, const T b)
{
    if (b == 0) { return std::pair<T, T>{1, 0}; }
    const auto p = extgcd(b, a % b);
    return {p.second, p.first - p.second * (a / b)};
}
template <typename T>
constexpr T inverse(const T a, const T mod = MOD) { return (mod + extgcd(a, mod).first % mod) % mod; }
int main()
{
    std::cin.tie(0);
    std::ios::sync_with_stdio(false);
    int N;
    std::cin >> N;
    assert(1 <= N and N < 2e5);
    ll P;
    std::cin >> P;
    assert(1 <= P and P < MOD);
    std::vector<ll> fact(2 * N + 1, 1), inv(2 * N + 1, 1);
    for (ll i = 2; i <= 2 * N; i++) { fact[i] = (fact[i - 1] * i) % MOD, inv[i] = ((MOD - MOD / i) * inv[MOD % i]) % MOD; }
    for (int i = 1; i <= 2 * N; i++) { (inv[i] *= inv[i - 1]) %= MOD; }
    std::vector<int> R(N, 0);
    for (int i = 0, a; i < N; i++) { std::cin >> a, assert(0 <= a and a < N), R[a]++; }
    ll ans = P, sum = 0;
    int zero = 0;
    for (int i = N - 1, k = 0; i >= 0; k += R[i], i--) {
        const int r = R[i];
        if (r == 0) { continue; }
        const ll Q = (P * r + k) % MOD;
        if (Q == 0) {
            sum = (r * fact[r + k - 1] % MOD) * inv[k] % MOD, zero++;
        } else {
            (sum += r * inverse(Q) % MOD) %= MOD;
            (((ans *= fact[r + k - 1] * inv[k] % MOD) %= MOD) *= Q) %= MOD;
        }
    }
    std::cout << (zero >= 2 ? 0LL : ans * sum % MOD) << std::endl;
}