#include <iostream>
#include <stack>
#include <fstream>

using namespace std;

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

long long n, k, i, de[5000001], suma, mi = 10000001, x;
deque<pair<long long, long long>> deq;

int main()
{
    in >> n >> k;

    for(i = 1; i <= k; i++)
    {
        in>>x;
        while(deq.empty() == false && deq.back().first >= x)
            deq.pop_back();

        deq.push_back(make_pair(x, i));
    }

    suma = deq.front().first;

    for(i = k + 1; i <= n; i++)
    {
        in>>x;
        while(deq.empty() == false && i - deq.front().second >= k)
            deq.pop_front();

        while(deq.empty() == false && deq.back().first >= x)
            deq.pop_back();

        deq.push_back(make_pair(x, i));

        suma += deq.front().first;
    }

    out<<suma;

    return 0;
}