#include <iostream>
#include <fstream>
#include <deque>

#define ll long long

using namespace std;

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

const int NMAX = 5e6;

int n, k;
int A[NMAX + 1];
deque<int> dq;

int main() {
    fin >> n >> k;
    for(int i = 1; i <= n; i++) {
        fin >> A[i];
    }

    ll sum = 0;
    for(int i = 1; i <= n; i++) {
        int j = max(i - k + 1, 1);
        while(!dq.empty() && A[i] <= A[dq.back()]) {
            dq.pop_back();
        }
        dq.push_back(i);
        if(dq.front() < j) {
            dq.pop_front();
        }
        //cout << i << " " << A[dq.front()] << '\n';
        if(i >= k) {
            sum += A[dq.front()];
        }
    }
    fout << sum;

    return 0;
}