#include <bits/stdc++.h>

using namespace std;

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

int n, k, i, x;
deque < pair <int, int> > dq;

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

    int ans = 0;

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

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

        dq.push_back({x,i});

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

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

    out << ans;

    return 0;
}