#include <fstream>
#include <deque>

using namespace std;

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

long long n, i, sum, k;
long long v[5000005];
deque <int> d;

int main()
{
    fin >> n >> k;
    for (i=1; i<=n; i++){
        fin >> v[i];
    }
    d.push_back(1);
    for (i=2; i<=n; i++){
        while (v[i] <= v[d.back()] && !d.empty()){
            d.pop_back();
        }
        d.push_back(i);
        while (d.front() == i - k && !d.empty()){
            d.pop_front();
        }
        if (i >= k){
            sum += v[d.front()];
        }
    }
    fout << sum;
    return 0;
}