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

using namespace std;

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

deque <int> deck;
const int NMAX = 5000000;
int v[NMAX+2];

int main()
{
    int n,k,sol=0;
    in>>n>>k;
    for(int i=1; i<=n; i++)
    {
        in>>v[i];
    }
    for(int i=1; i<k; i++)
    {
        while(deck.empty()!=1 && v[deck.back()]>=v[i])
        {
            deck.pop_back();
        }
        deck.push_back(i);
    }
    for(int i=k; i<=n; i++)
    {
        while(deck.empty()!=1 && i-k+1>deck.front())
            deck.pop_front();
        while(deck.empty()!=1 && v[i]<v[deck.back()])
            deck.pop_back();
        deck.push_back(i);
        sol+=v[deck.front()];
    }
    out<<sol;
}