#include <bits/stdc++.h>

using namespace std;

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

const int NMAX = 5e6 + 1;

int a[NMAX];

int main()
{
    int N, K;
    long long s = 0LL;
    fin >> N >> K;
    deque<int> dq;
    for (int i = 1; i <= N; ++i) {
        fin >> a[i];
        while (dq.size() && a[i] <= a[dq.back()]) {
            dq.pop_back();
        }
        dq.push_back(i);
        if (dq.front() <= i - K) {
            dq.pop_front();
        }
        if (i >= K)
            s += a[dq.front()];
    }
    fout << s;
    return 0;
}