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

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

deque<pair<int, int> > dq;

int main()
{
    int n, k, i, x;
    long long sum = 0;

    fin>>n>>k;
    for(i=1; i<=n; i++)
    {
        fin>>x;
        while(!dq.empty() && x < dq.back().first)
        {
            dq.pop_back();
        }
        dq.push_back({x, i});

        if(i >= k)
        {
            sum += dq.front().first;
            if(dq.front().second <= i - k + 1)
            {
                dq.pop_front();
            }
        }
    }

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