#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1000005;
inline int readint() {
  int res = 0, f = 1;
  char c = 0;
  while (!isdigit(c)) {
    c = getchar();
    if (c == '-') f = -1;
  }
  while (isdigit(c)) res = res * 10 + c - '0', c = getchar();
  return res * f;
}
int n, k, a[MAXN];
int stc[MAXN], nxt[MAXN], lst[MAXN], top;
inline int calc(int len) {
  int t = len / (k - 1);
  if (t == 0) return 0;
  long long res = 1ll *
                  (2 * len - 2 * k + 2 - 1ll * (t - 1) * (k - 1) % 1000000007) *
                  t / 2;
  return res % 1000000007;
}
int main() {
  n = readint(), k = readint();
  for (int i = 1; i <= n; i++) a[i] = readint();
  for (int i = 1; i <= n; i++) {
    while (top && a[stc[top]] <= a[i]) nxt[stc[top]] = i, top--;
    lst[i] = stc[top], stc[++top] = i;
  }
  for (int i = 1; i <= top; i++) nxt[stc[i]] = n + 1;
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    int l = lst[i], r = nxt[i];
    int tmp = calc(r - l - 1) - calc(i - l - 1) - calc(r - i - 1);
    tmp = (tmp % 1000000007 + 1000000007) % 1000000007;
    ans = (ans + 1ll * a[i] * tmp) % 1000000007;
  }
  printf("%d\n", ans);
  return 0;
}
