#include <bits/stdc++.h>
using namespace std;
const long double Pi = 3.14159265359;
const long long MOD = (long long)1e9 + 7;
const long long MAXN = (long long)1e6 + 10;
const long long INF = (long long)9223372036854775;
const long double EPS = (long double)1e-8;
long long dp[MAXN];
long long dpx[MAXN];
long long a[MAXN];
deque<long long> de;
stack<long long> s;
long long mk[MAXN];
long long lb[MAXN];
int main() {
  long long n, k;
  scanf("%lld", &n);
  scanf("%lld", &k);
  for (int i = 0; i < n; i++) scanf("%lld", &a[i]);
  for (int i = 0; i < k - 1; i++) {
    while (de.size() != 0) {
      if (a[de.back()] <= a[i])
        de.pop_back();
      else
        break;
    }
    de.push_back(i);
  }
  for (int i = k - 1; i < n; i++) {
    while (de.size() != 0) {
      if (a[de.back()] <= a[i])
        de.pop_back();
      else
        break;
    }
    de.push_back(i);
    if (i - de.front() >= k) de.pop_front();
    mk[i] = de.front();
  }
  de.clear();
  for (int i = 0; i < n; i++) {
    while (de.size() != 0) {
      if (a[de.back()] <= a[i])
        de.pop_back();
      else
        break;
    }
    if (de.size() == 0)
      lb[i] = -1;
    else
      lb[i] = de.back();
    de.push_back(i);
  }
  long long nex, cnt, pa;
  for (int i = k - 1; i < n; i++) {
    nex = lb[mk[i]];
    if (nex == -1) {
      dpx[i] = ((a[mk[i]]) * (i / (k - 1))) % MOD;
    } else {
      cnt = i - nex - 1;
      pa = cnt / (k - 1);
      dpx[i] = (dpx[i - (pa * (k - 1))] + ((a[mk[i]]) * pa)) % MOD;
    }
  }
  long long ans = 0;
  for (int i = 0; i < n; i++) ans = (ans + dpx[i]) % MOD;
  printf("%lld", ans);
  return 0;
}
