#include <iostream>
#include <fstream>
#include <list>
#include <utility>

int main() {
    std::ifstream fileIn("deque.in");
    std::ofstream fileOut("deque.out");

    std::list<std::pair<int, int>> myQ;

    int nV, nK;

    fileIn >> nV >> nK;

    long long sum(0);
    int aux;
    for (int i(1); i <= nV; i++) {
        fileIn >> aux;

        while (!myQ.empty() && myQ.front().first <= i - nK) {
            myQ.pop_front();
        }

        while (!myQ.empty() && myQ.back().second >= aux) {
            myQ.pop_back();
        }

        myQ.push_back(std::make_pair(i, aux));

        if (i >= nK) {
            sum += myQ.front().second;
        }
    }

    fileOut << sum;

    fileIn.close();
    fileOut.close();
    return 0;
}