#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

int a[5000005];
deque<int> deq;

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