#include <bits/stdc++.h>

using namespace std;

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

int main()
{
    int v[5000001], n, nr_el_secventa;
    deque<int> d;
    f >> n >> nr_el_secventa;
    for (int i=1; i<=n; i++)
        f>>v[i];
    long long sum=0;
    for (int poz=1; poz<=n; poz++)
    {
        while (!d.empty() && v[poz]<=v[d.back()]) d.pop_back(); 
        d.push_back(poz);    
        while (d.front() <= poz-nr_el_secventa ) d.pop_front(); 
        if (poz >= nr_el_secventa) sum = sum + v[d.front()]; 
    }
    g<<sum;
    
}