#include <bits/stdc++.h>

using namespace std;

#define MAXN 5000000

long long n, k, sum, v[MAXN];
vector<int> aux;
deque<int> dq;

int main() {
    ifstream cin("deque.in");
    ofstream cout("deque.out");

    cin >> n >> k;

    for (int i = 1; i <= n; i++) {
        cin >> v[i];
    }

    for (int i = 1; i <= n; i++) {
        while (!dq.empty() && (dq.back() >= v[i])) {
            dq.pop_back();
        }

        dq.emplace_back(v[i]);

        if (dq.front() == v[i - k]) {
            dq.pop_front();
        }

        if (i >= k) {
            sum += dq.front();
        }
    }

    cout << sum;
}