#include <bits/stdc++.h>
std::ifstream fin("deque.in");
std::ofstream fout("deque.out");
int n, k;
int deque[5000001], v[5000001];
void push_back(int deque[], int val, int &back){
  deque[++back] = val;
}
void pop_back(int deque[], int &back){
  back--;
}
void pop_front(int deque[], int val, int &front){
  front++;
}
int main(){
  int i, back = -1, front = 0;
  long long mins = 0;
  fin >> n >> k;
  for(i = 0; i < n; i++)
    fin >> v[i];
  push_back(deque, 0, back);
  for(i = 1; i < n; i++){
    while(v[i] <= v[deque[back]] && front <= back)
      pop_back(deque, back);
    push_back(deque, i, back);
    if(i >= k - 1)
      mins += v[deque[front]];
    if(i - k + 1 == deque[front])
        pop_front(deque, i, front);
  }
  fout << mins;
  return 0;
}