#include <bits/stdc++.h>

using namespace std;

const string FILENAME = "deque";

ifstream fin(FILENAME + ".in");
ofstream fout(FILENAME + ".out");

int n, k;
int a[5000001];
deque<int> d;
int main()
{
    long long ans = 0;
    fin >> n >> k;
    for(int i = 1; i <= n; i++)
        fin >> a[i];
    for(int i = 1; i <= n; i++)
    {
        while(!d.empty() && a[i] <= a[d.back()])d.pop_back();
        while(!d.empty() && d.front() <= i - k)d.pop_front();
        d.push_back(i);
        if(k <= i)
            ans += a[d.front()];
    }
    fout << ans << "\n";
    fin.close();
    fout.close();
    return 0;
}