#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 *in,*out;
long long sum=0;
typedef pair<int,int> ii;
class deq
{
public:
	void pop_front()
	{
		ciorba++;
	}
	void pop_back()
	{
		nurofen--;
	}
	bool empty()
	{
		return ciorba>nurofen;
	}
	void push_back(ii x)
	{
		nurofen++;
		ciulama[nurofen]=x;	
	}
	ii back()
	{
		return ciulama[nurofen];
	}
	ii front()
	{
		return ciulama[ciorba];
	}
private:
	ii ciulama[5000005];
	int ciorba,nurofen;
};
deq q;
int main()
{
	int i,k,n,x;
	in=fopen("deque.in","r");
	out=fopen("deque.out","w");
	fscanf(in,"%d%d",&n,&k);
	FOR(i,1,k-1)
	{
		fscanf(in,"%d",&x);
		while (!q.empty()&&q.back().fs>=x)
			q.popb();
		q.pb(mp(x,i));
	}
	sum=0;
	FOR(i,k,n)
	{
		fscanf(in,"%d",&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(in);
	fclose(out);
	return 0;
}