#include<iostream>
#include<fstream>
#include<deque>
using namespace std;

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

int n, k, v[5000001], i;
long long sol;
deque<int> coada;

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