#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cctype>
#include <cmath>
#include <string>
#include <algorithm>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <stack>
#include <cassert>
using namespace std;

#define PRO "deque"
void OpenFiles(int EVAL)
{
	if(EVAL)
	{
		char input[100] = PRO, output[100] = PRO;
		freopen(strcat(input, ".in"),"r",stdin);
		freopen(strcat(output,".out"),"w",stdout);
	} else
	{
		freopen("test.in","r",stdin);
		freopen("test.out","w",stdout);
	}
}

#define MAX 100001
#define INF 0xffffff

deque<pair<int,int> >d;

int main(int argv,char *args[])
{
	OpenFiles(argv==0);
	// start
	int n,k,x;
	long long s=0;
	scanf("%d %d",&n,&k);
	for(int i=1;i<=k;i++)
	{	
		scanf("%d",&x);
		while( d.size() > 0 && d.back().second >= x )d.pop_back();
		d.push_back(make_pair(i,x));
	}
	s += d.front().second;
	for(int i=k+1;i<=n;i++)
	{
		scanf("%d",&x);
		while( d.size() > 0 && d.back().second >= x )d.pop_back();
		while( d.size() > 0 && d.front().first <= i-k )d.pop_front();
		d.push_back(make_pair(i,x));
		s += d.front().second;
	}
	printf("%lld\n",s);
	return 0;
}