#include <bits/stdc++.h>
using namespace std;
const int INF = 1000 * 1000 * 1000;
long long n, m, k, x, y;
pair<long long, long long> a[1005000];
long long nx[1005000], pr[1005000];
long long cnt(long long l, long long r) {
  if (l > r) swap(l, r);
  long long sum = l / (k - 1);
  long long ans = 0;
  long long st = 1;
  ans += (st + (st + sum * (k - 1))) * (sum + 1) / 2;
  l -= sum * (k - 1);
  r -= sum * (k - 1);
  st += sum * (k - 1);
  long long dots_l = l;
  long long dots_r = min(r, k - 1);
  st -= (k - 1 - dots_l);
  st -= (k - 1 - dots_r);
  st += k - 1;
  if (st > 0)
    ans += st;
  else
    return ans;
  r -= dots_r;
  sum = r / (k - 1);
  ans += sum * st;
  r -= sum * (k - 1);
  st -= (k - 1 - r);
  if (st > 0)
    ans += st;
  else
    return ans;
  st -= (k - 1);
  if (st <= 0) return ans;
  sum = st / (k - 1);
  ans += (st + (st - sum * (k - 1))) * (sum + 1) / 2;
  return ans;
}
int main() {
  cin >> n >> k;
  for (int i = 1; i <= n; i++) {
    int x;
    scanf("%d", &x);
    a[i].first = x;
    a[i].second = i;
    nx[i] = i + 1;
    pr[i] = i - 1;
  }
  sort(a + 1, a + n + 1);
  long long ans = 0;
  for (int i = 1; i <= n; i++) {
    long long val = a[i].first;
    long long pos = a[i].second;
    long long np = nx[pos];
    long long pp = pr[pos];
    long long l = pos - pp - 1;
    long long r = np - pos - 1;
    ans += (cnt(l, r) - 1) % 1000000007 * val % 1000000007;
    nx[pr[pos]] = np;
    pr[nx[pos]] = pp;
  }
  cout << ans % 1000000007 << endl;
  return 0;
}
