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