#include <iostream>
#include <cstdio>
#include <fstream>
#include <unordered_map>
#include <vector>
#include <map>
#include <deque>

using namespace std;

int main() {
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);

    int n, k, x;
    long long ans = 0;
    cin >> n >> k;
    deque<pair<int, int>> dq;
    for(int i = 1; i <= n; i ++) {
        cin >> x;
        while(!dq.empty() && x < dq.back().first)
            dq.pop_back();
        dq.emplace_back(x, i);
        while(dq.front().second < i - k + 1)
            dq.pop_front();
        if(i >= k) {
            ans += dq.front().first;
        }
    }
    cout << ans << '\n';

    return 0;
}