#include <iostream>
#include <fstream>

using namespace std;

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

int n,k,v[5000005],dq[5000005];
long long int suma;

int main()
{
    int i,j;
    in >> n >> k;
    for (i=0; i<n; i++)
    {
        in >> v[i];
    }
    int st = 0,dr = -1;
    for (i=0; i<n; i++)
    {
        ///scot din st ceea ce nu mai e in sceventa ceruta
        if (st <= dr && dq[st] == i-k)
        {
            st++;
        }
        ///scot din dr ce e prost
        while (st <= dr && v[i] <= v[dq[dr]])
        {
           dr--;
        }
        dq[++dr] = i;
        if (i >= k-1)
        suma += v[dq[st]];
    }
    out << suma;
    return 0;
}