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

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

deque < pair < int, int > > q;
int n, k;


int main()
{
    fin >> n >> k;

    int el;
    long long sum = 0;

    for(int i = 1; i <= n; i++)
    {
        fin >> el;

        while(!q.empty() && q.back().first > el)
            q.pop_back();

        q.push_back({el, i});

        if(i >= k)
        {
            sum += q.front().first;

            if(q.front().second <= i - k + 1)
                q.pop_front();
        }
    }

    fout << sum;

    fin.close();
    fout.close();
    return 0;
}