#include <stdio.h>
#include <algorithm>
#include <cmath>
#include <cctype>
#include <cstring>
#include <vector>
#include <deque>
using namespace std;
#define Max 100001

deque<pair<int,int> >d;

int main()
{
	long long s=0;
	int n,k,x;
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
		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.front().first <= i-k)d.pop_front();
			while(d.size()>0 && d.back().second >= x)d.pop_back();
			d.push_back(make_pair(i,x));
			s+=d.front().second;
		}
		printf("%lld\n",s);
	return 0;
}