#include <bits/stdc++.h>

using namespace std;

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

#define int long long


deque < pair <int,int> > dq;

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

    int rez = 0;

    for(int i = 1; i <= n; i++)
    {
            int x;
            in >> x;

            if(!dq.empty())
            while(x <= dq.back().first && !dq.empty())
                dq.pop_back();

            dq.push_back({x,i});

            if(i >= k)
                rez += dq.front().first;

            if(dq.front().second + k - 1 == i)
            {
                dq.pop_front();
            }
    }


    out << rez;
    return 0;
}