#include <iostream>
#include <vector>
#include <algorithm>
using ll = long long;
constexpr ll MOD = 1000000007;
constexpr int MAX = 200000;
ll dp[MAX];
int R[MAX];
ll fact[2 * MAX + 1];
ll inv[2 * MAX + 1];

int main()
{
    std::cin.tie(0);
    std::ios::sync_with_stdio(false);
    int N;
    ll P;
    std::cin >> N >> P;
    std::fill(fact, fact + 2 * MAX + 1, 1), std::fill(inv, inv + 2 * MAX + 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; }
    for (int i = 0, a; i < N; i++) { std::cin >> a, R[a]++; }
    dp[0] = 1;
    for (int i = N - 1, k = 0, max = 0; i >= 0; k += R[i], i--) {
        const int r = R[i];
        if (r == 0) { continue; }
        const ll alpha = (r * fact[r + k - 1] % MOD) * inv[k] % MOD;
        const ll beta = (k * fact[r + k - 1] % MOD) * inv[k] % MOD;
        for (int j = max; j >= 0; j--) { (dp[j + 1] += alpha * dp[j] % MOD) %= MOD, (dp[j] *= beta) %= MOD; }
        max++;
    }
    for (int i = 0; i <= N; i++) { std::cerr << dp[i] << " "; }
    std::cerr << std::endl;
    ll ans = 0;
    for (ll i = 0, p = 1; i <= N; i++, (p *= P) %= MOD) { (ans += (i * p % MOD) * dp[i] % MOD) %= MOD; }
    std::cout << ans << std::endl;
}