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

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

int v[5000005], n, k;
long long sum;
deque < int > dq;

int main()
{
    fin >> n >> k;
    for (int i=0; i<n; i++)
        fin >> v[i];
    dq.push_front(0);
    for (int i=1; i<n; i++)
    {
        if (dq.front()==i-k)
        {
            dq.pop_front();
        }
        while(!dq.empty() && v[i]<v[dq.back()])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if (i>=k-1)
            sum+=v[dq.front()];
    }
    fout << sum;
    return 0;
}