#include <iostream>
#include <fstream>
#include <deque>
#define nMax 5000005

using namespace std;
int n, a[nMax], k, sum;
deque <int> deq;

void read()
{
    ifstream fin("deque.in");
    fin >> n >> k;
    for(int i = 1; i <= n; ++i)
        fin >> a[i];
}
void solve()
{
  for(int i = 1; i <= n; ++i){
    while(!deq.empty() && a[i] <= a[deq.back()]) deq.pop_back();
    deq.push_back(i);
    if(deq.front() == i - k) deq.pop_front();
    if(i >= k) sum += a[deq.front()];
    }
}
void write()
{
    ofstream fout("deque.out");
    fout << sum;
}
int main()
{
    read();
    solve();
    write();
    return 0;
}