#include <bits/stdc++.h>

using namespace std;

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

int v[5000001], n, nr_el_secventa;
deque<int> d;

int deq(){
    f >> n >> nr_el_secventa;
    long long sum=0;
    for (int poz=1; poz<=n; poz++)
    {
        f>>v[poz];
        
        while(!d.empty() and 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 += v[d.front()]; 
    }
    return sum;
}
int main()
{
    g<<deq();
    
}