#include <iostream>
#include <vector>
using ll = long long;
constexpr ll MOD = 1000000007;
template <ll mod = MOD>
class ModCombination
{
public:
    ModCombination(const std::size_t n) : fact(n + 1, 1), inv(n + 1, 1), inv_fact(n + 1, 1)
    {
        for (ll i = 2; i <= (ll)n; i++) { fact[i] = (fact[i - 1] * i) % mod, inv[i] = ((mod - (mod / i)) * inv[mod % i]) % mod, inv_fact[i] = (inv_fact[i - 1] * inv[i]) % mod; }
    }
    ll factorial(const std::size_t n) const { return fact[n]; }
    ll inverse(const std::size_t n) const { return inv[n]; }
    ll inverseFactorial(const std::size_t n) const { return inv_fact[n]; }

private:
    std::vector<ll> fact, inv, inv_fact;
};
int main()
{
    int N;
    ll B;
    std::cin >> N >> B;
    ModCombination<> mod(N);
    std::vector<ll> c(N + 1, 0);
    for (int i = 0; i < N; i++) {
        int S;
        std::cin >> S;
        c[N - S]++;
    }
    std::vector<ll> C = c;
    for (int i = 1; i <= N; i++) { C[i] += C[i - 1]; }
    ll p0 = 1, p1 = 0;
    for (int i = 0; i < N; i++) {
        const ll F = mod.factorial(C[i + 1]) * mod.inverseFactorial(C[i]) % MOD;
        const ll alpha = C[i + 1] == 0 ? 0 : (F * c[i + 1] % MOD) * mod.inverse(C[i + 1]) % MOD;
        const ll beta = C[i + 1] == 0 ? F : (F * C[i] % MOD) * mod.inverse(C[i + 1]) % MOD;
        const ll p0_ = p0;
        p0 = p0 * (alpha * B % MOD + beta) % MOD, p1 = ((p0_ * alpha) % MOD + p1 * (alpha * B + beta) % MOD) % MOD;
    }
    std::cout << p1 * B % MOD << std::endl;
}