#include <iostream>
#include <deque>
#include <stdio.h>
#include <fstream>
#include <vector>

using namespace std;

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

    int N, K, x;
    long long sum = 0;
    vector<int> v;

    fin >> N >> K;
    deque<int> dq;

    for (int i = 0; i < N; i ++) {
        fin >> x;
        v.push_back(x);
    }

    for(int i = 0; i < N; i++) {
        while (!dq.empty() && dq.back() <= i - K) {
            dq.pop_back();
        }

        while (!dq.empty() && v[dq.front()] > v[i]) {
            dq.pop_front();
        }

        dq.push_front(i);

        if (i >= K - 1) {
            sum += v[dq.back()];
        }
    }

    fout << sum;

    fin.close();
    fout.close();

    return 0;
}