// var STL

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

using namespace std;

deque <int> deck;

const int NMAX = 5000005;
int v[NMAX], k, n;

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

int main()
{
    int i;
    long long s=0;
    fin >> n >> k;
    for(i = 1; i <= n; i++){
        fin >> v[i];
    }
    for(i = 1; i <= n; i++){
        while(deck.size() > 0 && v[i] <= v[ deck.back() ])
            deck.pop_back();
        deck.push_back(i);
        if(deck.front() == i - k)
            deck.pop_front();
        if(i >= k)
            s += v[ deck.front() ];
    }
    fout << s;
    return 0;
}