#include <bits/stdc++.h>
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");

long long n, k, v[5000001];
deque <long long> dq;

int main()
{
    long long s = 0;
    fin >> n >> k;
    for (int i = 1; i <= n; i++)
        fin >> v[i];

    for (int i = 1; i <= k; i++)
    {
        while (!dq.empty() && v[i] <= v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
    }
    s += v[dq.front()];

    for (int i = k + 1; i <= n; i++)
    {
        while (!dq.empty() && v[i] <= v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if (!dq.empty() && i - dq.front() >= k)
            dq.pop_front();
        s += v[dq.front()];
    }

    fout << s;
    return 0;
}