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

int main() {
    int N, K;
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin >> N >> K;
    vector<int> A(N);

    for (int i = 0; i < N; i++) {
        fin >> A[i];
    }

    deque<int> dq;
    int sum = 0;

    for (int i = 0; i < N; i++) {
        while (!dq.empty() && A[dq.back()] >= A[i]) {
            dq.pop_back();
        }

        dq.push_back(i);

        if (i >= K - 1) {
            sum += A[dq.front()];
        }

        if (dq.front() <= i - K + 1) {
            dq.pop_front();
        }
    }

    fout << sum << endl;

    return 0;
}