#include <fstream>
#include <deque>

using namespace std;

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

int v[5000001];

int main()
{
    int n, k, s = 0;
    in >> n >> k;
    deque<int> d;
    for(int i = 0; i < n; i++) {
        in >> v[i];
        if(!d.empty() && d.front() == i - k) {
            d.pop_front();
        }
        while(!d.empty() && v[d.back()] >= v[i]) {
            d.pop_back();
        }
        d.push_back(i);
        if(i >= k - 1) { s += v[d.front()]; }
    }
    out << s;
    return 0;
}