#include <fstream>
#include <deque>
#include <climits>

using namespace std;

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

int n, k, sum, v[5000005];
deque<int> D;

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