#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

deque <long long> sir;
long long minim[50001];

int main() {
    long long n, k, number, min_value = 10000000, poz = 0, sum = 0;
    fin >> n >> k;
    for (int i = 1; i <= n; ++i) {
        fin >> number;
        sir.push_back(number);
    }
    while (sir.size() >= 3) {
        min_value = 10000000;
        for (int i = 0; i < k; ++i) {
            min_value = min(min_value, sir[i]);
        }
        minim[++poz] = min_value;
        sir.pop_front();
    }
    for (int i = 1; i <= poz; ++i) {
        sum += minim[i];
    }
    fout << sum;
}