#include <bits/stdc++.h>
using namespace std;

#define NMAX 5000004

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

int v[NMAX];

deque<int> deq;
int n, k;
long long rez;

int main () {
    fin >> n >> k;
    for (int i = 1; i <= n; i ++) {
        fin >> v[i];
    }
    for(int i = 1; i <= n; i++) {
        while (deq.empty() == false && v[i] <= v[deq.back()]) {
            deq.pop_back();
        }

        deq.push_back(i);
        if(i >= k) {
            rez += v[deq.front()];
            if(deq.front() == i - k + 1) {
                deq.pop_front();
            }
        }
    }

    fout << rez;

    return 0;
}