#include <bits/stdc++.h>
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
int main ()
{
    int n, k;
    long long sum = 0;
    fin >> n >> k;
    vector <int> v(n);
    deque <int> dq;
    for (int i = 0; i < n ; i++)
    {
        fin >> v[i];
        if(!dq.empty() && 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 << endl;
}