#include <iostream>
#include<deque>
#include<vector>
#include<fstream>

using namespace std;

int v[5000000];
int n, k;

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

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