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

using namespace std;

#define MAX 5000//010

int main()
{
    FILE *fin = fopen("deque.in", "r"), *fout = fopen("deque.out", "w");

    int N, K, n, v[MAX], minime[MAX];
    long long sum = 0;

    fscanf(fin, "%d %d", &N, &K);
    deque<int> dq;

    for (int i = 0; i < N; i ++) {
        fscanf(fin, "%d", &n);
        v[i] = n;
    }
/*
    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);

        minime[i] = dq.back();
    }

    for (int i = K - 1; i < N; i++) {
        sum += v[minime[i]];
    }*/

    fprintf(fout, "%d", sum);

    return 0;
}