#include <fstream>

using namespace std;

const int N = 5000000;

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

int v[N], d[N];
int main()
{
    int n, k, st, dr;
    long long s = 0;
    in >> n >> k;
    st = 0;
    dr = -1;
    for (int i = 0; i < n; i++)
    {
        in >> v[i];

        if (st <= dr && d[st] == i - k)
        {
            st++;
        }

        while (st <= dr && v[d[dr]] >= v[i])
        {
            dr--;
        }
        d[++dr] = i;
        if (i >= k - 1)
        {
            s += v[d[st]];
        }
    }
    in.close();
    out << s;
    out.close();
    return 0;
}