#include <iostream>
#include <fstream>
#include <deque>
#include <vector>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
using namespace std;

int main()
{
    int n,k,x, S=0;
    f>>n>>k;
    vector<int> v;
    deque<int> d;
    for (int i=0; i<n;i++)
    {
        f>>x;
        v.push_back(x);
    }
    d.push_back(0);
    for (int i=1;i<n;i++)
    {
        while (d.empty()==0 && v[i] <=v[d.back()])
            d.pop_back();
        d.push_back(i);
        if (d.front() == i-k)
            d.pop_front();

        if (k-1 <= i)
            S+=v[d.front()];
    }
    g<<S;
    f.close();
    g.close();
    
}