#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

int main() {
    int n, k;
    cin >> n >> k;
    vector<int> v(n);
    for (auto &&i : v) scanf("%d", &i);
    int S = accumulate(v.begin(),v.end(), 0);
    ll ans = 0, val = 1;
    reverse(v.begin(),v.end());
    for (int i = 0; i < n; ++i) {
        ans = (ans + v[i]*val)%S;
        val = val*k%S;
    }
    cout << ans << "\n";
    return 0;
}