#include <iostream>
#include <deque>
#include <utility>
#include <fstream>
using namespace std;

int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    deque < pair<long long,long long> >my_deq;
    int n,k;
    long long s=0,x,i;
    f>>n>>k;
    for (i=0;i<n;i++)
    {
        f>>x;
        while (!my_deq.empty()&&my_deq.back().first>=x)
        {
            my_deq.pop_back();
        }
        my_deq.push_back(make_pair(x,i));
        if (my_deq.front().second==i-k)
            my_deq.pop_front();
        if (i>=k-1)
            s+=my_deq.front().first;
    }
    g<<s;
    f.close();
    g.close();
    return 0;
}