#include <bits/stdc++.h>

using namespace std;



int main()
{
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");

    int n, k, front = 0, back = -1;
    long long sum = 0;

    fin >> n >> k;
    int v[n+1], deq[n];

    for (int i = 0; i < n; i++)
        fin >> v[i];
    fin.close();

    for (int i = 0; i < n; i ++)
    {
        while (front <= back && v[i] < v[deq[back]])
            back--;
        back++;
        deq[back] = i;
        if (deq[front] == i-k)
            front++;
        if (i >= k-1)
            sum += v[deq[front]];

    }

    fout<< sum;
    fout.close();
    return 0;


}