#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

const int MAXN = 5000100;
const long long inf = (1LL << 63) - 1;

int values[MAXN];
deque< int > d;

void insert(int poz)
{
    while (!d.empty() && values[d.back()] > values[poz])
        d.pop_back();
    d.push_back(poz);
}

int get_min(int curIndex)
{
    while(!d.empty() && d.front() < curIndex)
        d.pop_front();
    return values[d.front()];
}

int n,k;

int main()
{
    fin>>n>>k;
    for (int i = 1; i <= n; ++i)
        fin >> values[i];

    for (int i = 1; i <= k; ++i)
        insert(i);

    long long sum = 0;

    for (int i = k + 1; i <= n + 1; ++i)
    {
        sum += get_min(i - k);
        insert(i);
    }


    fout<<sum;

}