#include <bits/stdc++.h>

#define llg long long

std::ifstream input ("deque.in");
std::ofstream output("deque.out");

int N, K;
std::deque <std::pair <int, int>> deque;

int main()
{
    input >> N >> K;
    llg sum = 0;
    for (int i=1, x; i<=N; ++i) {
        input >> x;
        while (!deque.empty() && deque.back().second <= i-K) deque.pop_back();
        while (!deque.empty() && deque.front().first >= x) deque.pop_front();
        deque.push_front({x, i});
        if (i >= K) sum += 1ll*deque.back().first;
    }   output << sum << '\n';

    return 0;
}