#include <fstream>
#include <deque>
#define MAXN 5000001

using namespace std;

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

int v[MAXN];

int main() {
    deque<int> d;
    int n, k;
    long long sum = 0;
    fin >> n >> k;
    for (int i = 1; i <= n; ++i) {
        fin >> v[i];
    }
    for (int i = 1; i <= n; ++i) {
        while (!d.empty() && v[i] <= v[d.back()]) {
            d.pop_back();
        }
        d.push_back(i);
        if (d.front() == i - k) {
            d.pop_front();
        }
        if (i >= k) {
            sum += v[d.front()];
        }
    }
    fout << sum << "\n";
    return 0;
}

/*
----------------------------------------------------------------------
    // don't forget about the case where there aren't enough k numbers
    while (d[pos] != MARK  && d[k - 1] != MARK) {
        if (d[pos] < min) {
            min = d[pos];
        }
        if (pos == k - 1) {
            d.push_back(MARK);
            d.push_back(min);
            d.pop_front();
            min = INT_MAX;
            pos = -1;
        }
        ++pos;
    }
    while (d.front() != MARK) {
        d.pop_front();
    }
    for (int i = 0; i < d.size(); ++i) {
        if (d[i] != MARK) {
            sum += d[i];
        }
    }
    fout << sum;
----------------------------------------------------------------------

#include <fstream>
#include <iostream>
#define MAXN 5000001

using namespace std;

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

int v[MAXN], deq[MAXN];

int main() {
    int n, k, front = 1, back = 0;
    long long sum = 0;
    fin >> n >> k;
    for (int i = 1; i <= n; i++) {
        fin >> v[i];
    }
    for (int i = 1; i <= n; i++) {
        while (front <= back && v[i] <= v[deq[back]]) {
            --back;
        }
        deq[++back] = i;
        if (deq[front] == i - k) {
            ++front;
        }
        if (i >= k) {
            sum += v[deq[front]];
        }
    }
    cout << sum << "\n";
    return 0;
}
*/