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

using namespace std;

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

deque<int> dq;

int main()
{
    int n, k;
    f>>n>>k;
    int v[n];
    int s=0;
    for(int i=0; i<n; i++)
    {
        f>>v[i];
        if(!dq.empty() and dq.front() == i-k)
            dq.pop_front();
        while(!dq.empty() and v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i>=k-1)
            s+=v[dq.front()];
    }
    g<<s;

    return 0;
}