#include <bits/stdc++.h>
using namespace std;
ifstream f ("deque.in");
ofstream g ("deque.out");
deque <pair<int, int>> mini;
long long n, k, sum, v;
int main()
{

    f >> n >> k;
    for (int i = 1; i <= n; i++)
    {
        f >> v;
        while (!(mini.empty()) && v <= mini.back().first)
        {
            mini.pop_back();
        }
        mini.push_back({v, i});

        if (i-k == mini.front().second)
            mini.pop_front();


        if(i >= k)

            sum += mini.front().first;
    }
    g<<sum;

    return 0;
}