#include <fstream>

using namespace std;

int v[5000001], d[5000001];
ifstream f("deque.in");
ofstream g("deque.out");
int main()
{
    int st = 0, dr = -1, n, k;
    long long sum = 0;

    f >> n >> k;
    for (int i = 0; i < n; i++)
    {
        f >> v[i];
        if (st <= dr && d[st] == i - k)
            st++;
        while (st <= dr && v[i] <= v[d[dr]])
            dr--;
        d[++dr] = i;
        if (i >= k-1)
            sum += v[d[st]];
    }
    g << sum;
    return 0;
}