#include <bits/stdc++.h>
#define N_MAX 5000005

using namespace std;

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

int N, K, x, v[N_MAX];
deque < int > DQ;

long long sum;

int main()
{
    fin >> N >> K;
    for (int i = 1; i <= N; i++)
        fin >> v[i];

    DQ.push_front(1);
    for (int i = 2; i <= N; i++)
    {
        while (DQ.size() && v[DQ.back()] > v[i])
            DQ.pop_back();
        DQ.push_back(i);

        if (i >= K)
        {
            if (i - DQ.front() == K)
                DQ.pop_front();
            sum += v[DQ.front()];
        }
    }

    fout << sum << "\n";
    return 0;
}