#include <bits/stdc++.h>
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");
const int Nmax = 5000005;
int n,k,sum,a[Nmax],i;
deque<int> deq;


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

        //elimin nr outdated
        if(!deq.empty() && deq.front() <= i-k)
            deq.pop_front();

        while(!deq.empty() && a[i] < a[deq.back()] )
        {
            deq.pop_back();
        }

        deq.push_back(i); //pun indicele in deque

        if(i>=k)
        {
            sum += a[deq.front()];
        }
    }
    fout<<sum;
    return 0;
}