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

using namespace std;

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

#define ll long long

int n, k;
deque< pair<int, int> > q;
ll rez;

int main(){
	int i, x;
	fin >> n >> k;
	for(i = 1; i <= n; i++){
		if(i > k && q.front().second == i - k) q.pop_front();
		fin >> x;
		while(!q.empty() && x <= q.back().first) q.pop_back();
		q.push_back(make_pair(x, i));
		if(i >= k) rez += q.front().first;
	}
	fout << rez;
}