#include <bits/stdc++.h>
#include <fstream>
#include<iostream>
using namespace std;
ifstream f("deque.in");
ofstream o("deque.out");

 int v[5000005],dq[5000005];
int main()
{
long long rez;
int n,k;
int a,b,t;

    f>>n;
    f>>k;
	for(int i=1;i<=n;i++) f>>v[i];
	a=1,b=0;
	for(int i=1;i<=n;i++)
	{
	    while(a<=b && v[i]<=v[dq[b]]) {b=b-1;}
        dq[++b]=i;
        t=k-i;
        if(dq[a]==t) {a=a+1;}
        if(k<=i) rez=rez+v[dq[a]];
	}
	o<<rez;
	return 0;
}