#include <bits/stdc++.h>
#define ll long long 

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

int n, k;
ll a[5000005];
ll ans;
deque<int> q;

int main() {
    in >> n >> k;
    for (int i = 1; i <= n; i++) {
        in >> a[i];
    }

    for (int i = 1; i <= n; i++) {
        while (!q.empty() && a[i] < a[q.back()])
            q.pop_back();
        q.push_back(i);
        
        if (i > k) {
            while (!q.empty() && q.front() <= i - k)
                q.pop_front();
        }

        if (i >= k)
            ans += a[q.front()];
    }

    out << ans;

    return 0;
}