#include <bits/stdc++.h>

using namespace std;

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

const int n_max = 5000005;
int v[n_max];
int main()
{
    int n, k;
    fin >> n >> k;
    for (int i = 1; i <= n; i++)
    {
        fin >> v[i];
    }
    deque<int> dq;
    long long sum = 0;
    for (int i = 1; i <= n; i++)
    {
        while (!dq.empty() && v[i] <= v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(dq.front() == i-k)
            dq.pop_front();
        if(i >= k)
            sum = sum + v[dq.front()];
    }
    fout<<sum;
    return 0;
}