#include <bits/stdc++.h>

using namespace std;

#define MAXN 5000000

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

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

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

    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;
}