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

using namespace std;

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

deque<int> D;

long long n, k, a[5000001];
long long sum;

void citire()
{
    f>>n>>k;
    for (int i=0; i<n; i++)
        f>>a[i];
}

void parcurgere()
{
    D.push_back(0);
    for (int i=1; i<n; i++)
        {
        while (!D.empty() && a[i]<a[D.back()] )
            D.pop_back();
        D.push_back(i);
        if (i>=k-1)
        {
            if (D.front()<=i-k)
                D.pop_front();
            sum+=a[D.front()];
        }
    }
}

int main()
{
    citire();
    parcurgere();
    g<<sum;
    return 0;
}