#include <bits/stdc++.h>

using namespace std;

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

int main() {
    int N, K;
    fin >> N >> K;

    deque<pair<int, int>> dq;
    long long sum = 0;

    for (int i = 1; i <= N; i++) {
        int x;
        fin >> x;

        while (!dq.empty() && dq.back().first >= x)
            dq.pop_back();

        dq.push_back({x, i});

        while (!dq.empty() && dq.front().second <= i - K)
            dq.pop_front();

        if (i >= K)
            sum += dq.front().first;
    }

    fout << sum;
    return 0;
}