#include <bits/stdc++.h>
#define ll long long
#define mod 1999999973

using namespace std;

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

int n, k, a[5000100];
deque <int> dq;
long long ans;

int main(){
	in >> n >> k;
	for(int i = 1; i <= n; i++)
		in >> a[i];
	for(int i = 1; i <= k; i++){
		while(dq.size() && a[i] <= a[dq.back()])
			dq.pop_back();
		dq.push_back(i);
	}
	ans += a[dq.front()];
	for(int i = k + 1; i <= n; i++){
		while(dq.size() && a[i] <= a[dq.back()])
			dq.pop_back();
		dq.push_back(i);
		while(dq.front() <= i - k)
			dq.pop_front();
		ans += a[dq.front()];
	}
	out << ans;
	return 0;
}