#include<fstream>
#include<iostream>
#include<deque>
#define MAX_N 5000000
using namespace std;

int n, k, v[MAX_N + 1];
deque<int>dq;

int main() {
    int i;
    long long int sum;
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin >> n >> k;
    for(i = 0; i < n; i++)
        fin >> v[i];
    sum = 0;
    for(i = 0; i < n; i++) {
        if(!dq.empty() && dq.front() == i - k)
            dq.pop_front();
        while(!dq.empty() && v[i] <= v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i >= k - 1) {
            //cout << v[dq.front()] << " ";
            sum = sum +  v[dq.front()];
        }
    }
    fout << sum << "\n";
    fin.close();
    fout.close();
    return 0;
}