#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

const int nmax=5000002;
typedef long long itneger;

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

int n, k;
deque<int> dsh;
itneger sum=0, a[nmax];

int main()
{
	fin>>n>>k;
	for(int i=0; i<n; i++)
    {
        fin>>a[i];
		while(!dsh.empty() && a[i]<=a[dsh.back()]) dsh.pop_back();
		dsh.push_back(i);
        if(dsh.front()<i-k+1)
            dsh.pop_front();
        if(i>=k-1)
            sum+=a[dsh.front()];
	}
	cout<<sum;
	return 0;
}