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

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

const int MAX_SIZE = 5000001;
int v[MAX_SIZE];

int main() {
    int n, k;
    fin >> n >> k;
    for (int i = 1; i <= n; ++i) {
        fin >> v[i];
    }
    int result = 0;
    for (int i = 1; i <= n - k + 1; ++i) {
        int minimum = *min_element(v + i, v + i + k);
        //cout << minimum << " ";
        result += minimum;
    }
    fout << result << " ";
    return 0;
}