#include <bits/stdc++.h>

using namespace std;


class Node
{
public:
    int val;
    int ind;

public:
    void initialize(int x, int y)
    {
        val = x;
        ind = y;
    }

    Node()
    {}

    Node(int x, int y)
    {
        initialize(x, y);
    }
};

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

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

    deque <Node> deq;
    int x;
    long long int sum = 0;

    for(int i = 0; i < n; i++)
    {
        fin>>x;

        if(!deq.empty() && deq.front().ind <= i - k)
            deq.pop_front();

        while(!deq.empty() && x < deq.back().val)
            deq.pop_back();

        deq.push_back(Node(x, i));

        if( i + 1 >= k)
            sum += deq.front().val;

    }

    fout<<sum<<'\n';

    return 0;
}