#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

ifstream f ("deque.in");
ofstream g ("deque.out");
deque< pair< int, int > > d;
int n, k;

inline void DeleteFirst(int currentPosition, int k)
{
    if (!d.empty() && d.front().second <= currentPosition - k)
        d.pop_front();
}

inline void DeleteBiggerValues(int value)
{
    while (!d.empty() && d.back().first >= value)
        d.pop_back();
}
int main()
{
    f >> n >> k;
    long long sum = 0, x;
    f >> x;
    d.push_back(make_pair(x, 1));
    for (int i = 2; i < k; i++)
    {
        f >> x;
        DeleteBiggerValues(x);
        d.push_back(make_pair(x, i));
    }
    for (int i = k; i <= n; i++)
    {
        f >> x;
        DeleteFirst(i, k);
        DeleteBiggerValues(x);
        d.push_back(make_pair(x, i));
        sum += d.front().first;
    }
    g << sum;
    return 0;
}