#include <iostream>
#include <fstream>

int v[5000000];
int dq[5000000];

using namespace std;

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

int main()
{
    int n, k, i, st = 0, dr = -1;
    long long sum = 0;
    fin >> n >> k;
    for (i = 0; i < n; i++)
    {
        fin >> v[i];
        if (dq[st] == i - k)
            st++;
        while (st <= dr && v[i] <= v[dq[dr]])
            dr--;
        dq[++dr] = i;
        if (i >= k - 1)
            sum += v[dq[st]];
    }
    fout << sum;
    return 0;
}