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

int n, k, currentMin, a[5000000];
long long minsSum;

int main() {
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin >> n >> k;
    for (int i = 0; i < n; ++i) {
        fin >> a[i];
    }
    for (int i = 0; i <= n - k; ++i) {
        currentMin = a[i];
        for (int j = i; j < i + k; ++j) {
            currentMin = min(currentMin, a[j]);
        }
        minsSum += currentMin;
    }
    fout << minsSum;
    return 0;
}