#include <iostream>
#include <fstream>
#include <deque>

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

const int MAXN = 5000000;
int n, k, v[MAXN];
long long sum;

deque<int> d;

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

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

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