#include <bits/stdc++.h>

#define ll long long
#define M 666013

using namespace std;

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

ll n, k, x, sum;
deque<pair<int, int>> deq;

int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i++)
    {
        fin >> x;
        while(!deq.empty() && x <= deq.front().first)
            deq.pop_front();
        deq.push_front({x, i});

        while(!deq.empty() && i - k >= deq.back().second)
            deq.pop_back();

        if(i >= k)
            sum += deq.back().first;
    }
    fout << sum;

    return 0;
}