#pragma GCC optimize("O3,unroll-loops")

#include <fstream>
#include <iostream>
#include <deque>

using namespace std;
using ll = long long;

int fp() {
    int ch, t = 1, n = 0;
    while ((ch = getchar_unlocked()) && !isdigit(ch) && ch != '-');

    if (ch == '-')
        t = -1;

    if (isdigit(ch))
        n = ch - '0';

    while ((ch = getchar_unlocked()) && isdigit(ch))
        n = n * 10 + ch - '0';

    return t * n;
}

int main() {
    freopen("deque.in", "r", stdin);
    ofstream g("deque.out");
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n = fp(), k = fp();

    deque<pair<int, int>> Q;

    for (int i = 0, x; i < k; ++i) {
        x = fp();
        while (!Q.empty() && Q.back().first > x)
            Q.pop_back();

        Q.emplace_back(x, i);
    }

    ll sum = Q.front().first;

    for (int i = k, x; i < n; ++i) {
        x = fp();
        while (!Q.empty() && Q.front().second <= i - k)
            Q.pop_front();

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

        Q.emplace_back(x, i);
        sum += Q.front().first;
    }

    g << sum << '\n';
}