#include <iostream>
#include <fstream>
#include <deque>
#define ll long long
#define NMAX 5000000

using namespace std;

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

int n, k, v[NMAX+10];
ll ans;
deque <int> dq;

int main()
{
	fin >> n >> k;
	for(int i=1; i<=n; i++)
		fin >> v[i];
	for(int i=1; i<=n; i++)
		{	while(!dq.empty() && v[i] <= v[dq.back()])
				dq.pop_back();
			dq.push_back(i);
			if(i < k) continue;
			ans += (ll)v[dq.front()];
			while(!dq.empty() && dq.front() <= i - k + 1)
				dq.pop_front();
		}
	fout << ans << '\n';
	return 0;
}