#include<cstdio>
#include<utility>
#include<deque>
#include<algorithm>
using namespace std;
int main()
{
	deque< pair<int,int> > a;
	long long s=0;
	int i,n,x,k;
freopen("deque.in","r",stdin);
freopen("deque.out","w",stdout);
scanf("%d%d",&n,&k);
for(i=1;i<k;i++)
{
	scanf("%d",&x);
	while((!a.empty())&&(a.back().first>x)) a.pop_back();
	a.push_back(make_pair(x,i));
}
for(i=k;i<=n;i++)
{
	scanf("%d",&x);
	while((!a.empty())&&(a.back().first>x)) a.pop_back();
	a.push_back(make_pair(x,i));
    if(a.front().second==i-k) a.pop_front();
    s=s+a.front().first;
}
printf("%lld",s);
return 0;
}