#include <iostream>
#include <fstream>
#include <deque>
#define MAX 5000001

using namespace std;

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

int n, k;
int v[MAX];
long long sum;

int main()
{
    fin >> n >> k;
    deque <int> dq;
    for (int i = 1; i <= n; i++)
    {
        fin >> v[i];
        if (!dq.empty() && i - k == dq.front())
            dq.pop_front();
        while (!dq.empty() && v[i] < v[dq.back()])
        {
            dq.pop_back();
            if (dq.empty())
                break;
        }
        dq.push_back(i);
        if (i >= k)
            sum += v[dq.front()];
    }
    fout << sum;
    return 0;
}