#include <bits/stdc++.h>

using namespace std;

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

int n, k, v[5000001];
long long sum;

void cautare(int i) {
    int minim = 10000001;

    for (int j = i; j < i+k; ++j)
        minim = min(minim, v[j]);

    sum += minim;
}

int main() {
    in >> n >> k;
    for (int i = 0; i < n; ++i)
        in >> v[i];

    for (int i = 0; i < n; ++i)
        cautare(i);

    out << sum;
    return 0;
}