#include <fstream>
#include <deque>
#define DMAX 5000002
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");

void citire();
void rez();

int n, k;
deque <int> dq;
int a[DMAX];
long long int S;

int main()
{
    citire();
    rez();
    fout<< S<< '\n';
    
    fin.close();
    fout.close();
    return 0;
}

void citire()
{
    int i;
    fin>> n>> k;
    for (i=1; i<=n; i++) fin>> a[i];
}

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