#include <bits/stdc++.h>

using namespace std;

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

const int SIZE = 5e6 + 1;

int x, n, k;
int a[SIZE];
deque<int> dq;
long long sum;

int main()
{
    ios_base::sync_with_stdio(false);
    fin.tie(nullptr);

    fin >> n >> k;
    for(int i = 1; i <= n; ++i)
        fin >> a[i];

    //simulam pentru prima secv (1..k)

    for(int i = 1; i <= k; ++i)
    {
        while(!dq.empty() && a[dq.back()] >= a[i])
            dq.pop_back();

        dq.push_back(i);
    }

    sum += a[dq.front()];

    //analog pentru celelate secvente, dar acum eliminam front-ul cand paraseste secventa

    for(int i = k + 1; i <= n; ++i)
    {
        while(!dq.empty() && a[dq.back()] >= a[i])
            dq.pop_back();

        dq.push_back(i);

        if(dq.front() == i - k)
            dq.pop_front();

        sum += a[dq.front()];
    }

    fout << sum;

    return 0;
}