#include <bits/stdc++.h>

using namespace std;

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

#define dim 5000001

int a[dim];
deque <int> deq;

int main()
{
    int n, k;
    in >> n >> k;

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

    int Front = 1, Back = 0;
    long long sum = 0;

    for (int i=1; i<=n; i++)
    {
        while (!deq.empty() && a[i] <= a[deq.back()])
            deq.pop_back();

        deq.push_back(i);

        if (deq.front() == i-k)
            deq.pop_front();

        if (i>=k)
            sum += a[deq.front()];
    }

    out << sum;

    return 0;
}