#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000000], my_deque[5000000];

int main() {
    int n, k;
    long long sum = 0;
    fin >> n >> k;
    for (int i = 0; i < n; ++i) {
        fin >> v[i];
    }
    int pos_1 = 0, pos_2 = 0;
    my_deque[0] = 0;
    for (int i = 1; i < n; ++i) {
        if (v[i] < v[my_deque[pos_2]]) {
            my_deque[pos_2] = i;
            while (pos_2 > pos_1 && v[my_deque[pos_2]] < v[my_deque[pos_2 - 1]]) {
                my_deque[pos_2 - 1] = my_deque[pos_2];
                pos_2--;
            }
        } else {
            my_deque[++pos_2] = i;
        }
        if (i >= k - 1) {
            if (my_deque[pos_1] < i - k + 1) {
                pos_1++;
            }
            sum += v[my_deque[pos_1]];
        }
    }
    fout << sum;
    return 0;
}