#include <cstdio>
#include <vector>
#include <queue>
#include <stack>
#include <list>
#include <set>
#include <algorithm>
#include <utility>
#include <string>
#include <functional>
#include <sstream>
#include <fstream>
#include <iostream>
using namespace std;
#define FOR(i,a,b) for (i=a;i<=b;i++)
#define fori(it,v) for (it=(v).begin();it!=(v).end();it++)
#define pb push_back
#define mp make_pair
#define fs first
#define ss second
#define all(c) c.begin(),c.end()
#define pf push_front
#define popb pop_back
#define popf pop_front
FILE *out;
string *s;
ifstream fin("deque.in");
istringstream in;
long long sum=0;
typedef pair<int,int> ii;
deque<ii> q;
int main()
{
	int i,k,n,x;
	s=new string;
	getline(fin,*s,'\0');
	in.str(*s);
	delete s;
	out=fopen("deque.out","w");
	in>>n>>k;
	FOR(i,1,k-1)
	{
		in>>x;
		while (!q.empty()&&q.back().fs>=x)
			q.popb();
		q.pb(mp(x,i));
	}
	sum=0;
	FOR(i,k,n)
	{
		in>>x;
		while (!q.empty()&&i-q.front().ss>=k)
			q.popf();
		while (!q.empty()&&q.back().fs>=x)
			q.popb();
		q.pb(mp(x,i));
		//printf("%d\n",q.front().fs);
		sum+=(long long )q.front().fs;

	}
	fprintf(out,"%lld\n",sum);
	fclose(out);
	return 0;
}