#include <fstream>
#include <iostream>
#include <vector>
#include <deque>
#define NMAX 5000005

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

int N, K;
long long suma;
vector <int> v(NMAX);
deque  <int> d;

void Read(){
  in >> N >> K;
  for(int i = 1; i <= N; ++i)
    in >> v[i];
}

void Solve(){
  for(int i = 1; i <= N; ++i){
    while(!d.empty() && v[i] <= v[d.back()])
      d.pop_back();
    d.push_back(i);
    if(i - d.front() >= K)
        d.pop_front();
    if(i >= K)
      suma += v[d.front()];
  }
  out << suma << "\n";
}

int main() {
  Read();
  Solve();
  return 0;
}