#include <bits/stdc++.h>
using namespace std;

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

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

int main()
{
    long long sol = 0;
    fin >> n >> k;
    for (int i = 1; i <= k; i++)
    {
        fin >> a[i];
        while (!dq.empty() && dq.back() > a[i])
            dq.pop_back();
        dq.push_back(a[i]);
    }
    sol += dq.front();
    for (int i = k + 1; i <= n; i++)
    {
        fin >> a[i];
        if (a[i - k] == dq.front()) dq.pop_front();
        while (!dq.empty() && dq.back() > a[i])
            dq.pop_back();
        dq.push_back(a[i]);
        sol += dq.front();
    }
    fout << sol << "\n";
    fin.close();
    fout.close();
    return 0;
}
/**

-7
9
2
4
-1
5
6
7
1

dq = 1

*/