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

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

deque <int> q;
int a[5000001];

void elimina (int i) {
    while (!q.empty() && a[i] <= a[q.back()]) q.pop_back();
}

int main() {
    int n, k;
    int i;
    int s = 0;

    fin >> n >> k;
    for (i = 1; i <= n; ++i) fin >> a[i];


    for (i = 1; i <= n; ++i) {
        elimina(i);
        q.push_back(i);

        if (q.front() == i - k) q.pop_front();

        if (i >= k) s += a[q.front()];
    }

    fout << s << '\n';

    return 0;
}