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

using namespace std;

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

long long s;
deque<int> deq;
int n,k,a[5000001],i;

int main()
{
    in>>n>>k;
    for(i=1;i<=n;i++)
        in>>a[i];

    for(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) s+=a[deq.front()];
    }

    out<<s;
    return 0;
}