#include <iostream>
#include <fstream>
using namespace std;

using namespace std;
ifstream f ("deque.in");
ofstream g ("deque.out");
int main(){
    long long n, k;
    f >> n >> k;
    long  long suma = 0;
    int dq[5000001], aux[5000001];
    int front = 0, back = -1;
    for (int i = 0; i < n; i++)
        f>>aux[i];

    for (int i = 0; i < n; i++){
        while ( front <= back && aux[i] <= aux[dq[back]])
            back--;
        dq[++back] = i;
        if (dq[front] == i- k + 1)
            front ++;
        if (i >= k)
            suma+= aux[dq[front]];

    }
    g << suma;
}