#include<bits/stdc++.h>
#define in f
#define out g
using namespace std;

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


int n;
int k;
int v[5000001];
int counter;
int aux;
int s;

int main() {

    in >> n;
    in >> k;

    for(int i = 1; i <= n; i++) {
        in >> v[i];
    }
    aux = v[1];
    for(int i = 1; i <= n; i++) {
        counter++;
        aux = min(v[i], aux);
        if(counter == k) {
            s = s + aux;
            if(aux == v[i - k + 1]) {
                counter = 0;
                aux = v[i - k + 2];
                i = i - k + 1;
            } else {
                counter--;
            }
        }
    }
    out << s;
}