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

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

long long suma;
int N, K;
deque< pair<int, int> > qu;

int main()
{
    int x;
    in >> N >> K;
    for (int i = 1; i <= N; i++)
    {
        in >> x;
        while (!qu.empty() && qu.back().first >= x) qu.pop_back();
        qu.push_back(make_pair(x, i));
        if (qu.front().second == i-K) qu.pop_front();
        if (i >= K) suma += qu.front().first;
    }
    out << suma;
    return 0;
}