#include <fstream>
#include <deque>
#define dim 5000005
using namespace std;
ifstream in ("deque.in");
ofstream out("deque.out");
int v[dim], q[dim], n, k;
void deck()
{
    int st = 1, dr = 0;
    long long sol = 0;
    for (int i = 1; i <= n; i++) {
        while(st <= dr && v[i] <= v[q[dr]])
            dr--;
        q[++dr] = i;
        if (q[st] == i - k)
            st++;
        if (i >= k)
            sol += v[q[st]];
    }
    out << sol;
}
int main()
{
    in >> n >> k;
    for (int i = 1; i <= n; i++)
        in >> v[i];
    deck();
    return 0;
}