#include <bits/stdc++.h>

using namespace std;

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

#define int long long

int x, n, k, sum;

deque < pair <int, int> > d;

signed main()
{
    fin >> n >> k;

    for (int i = 1; i <= n; i ++)
    {
        fin >> x;

        while (!d.empty() && d.back().first > x)
            d.pop_back();

        d.push_back({x, i});

        if (d.front().second <= i - k)
            d.pop_front();

        if (i >= k)
            sum += d.front().first ;
    }

    fout << sum;

    return 0;
}