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

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

vector<int> v;

int main() {
    int n, k;
    fin >> n >> k;
    long long sum = 0;
    for (int i = 1; i <= n; ++i) {
        int elem;
        fin >> elem;
        v.push_back(elem);
        if (i >= k) {
            int minVal = *min_element(v.end() - k, v.end());
            sum += minVal;
        }
    }
    fout << sum << '\n';
    return 0;
}