#include <iostream>
#include <fstream>
#include <deque>
#include <vector>
using namespace std;
deque <int> deque1,deque2;
int main()
{
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");
    int n,k,nr,i,sum=0;
    fin>>n>>k>>nr;
    deque1.push_back(nr);
    deque2.push_back(1);
    for(i=2;i<=n;i++)
    {
        fin>>nr;
        while(!deque1.empty()&&deque1.back()>=nr)
        {
            deque1.pop_back();
            deque2.pop_back();
        }
        deque1.push_back(nr);
        deque2.push_back(i);
        if(i>=k)
        {
            if(deque2.front()<i-k+1)
            {
                deque1.pop_front();
                deque2.pop_front();
            }
            sum+=deque1.front();
        }
    }
    fout<<sum;
    return 0;
}