#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque<pair<long long,int>>Q;
int main()
{
   int n,i,k;
   long long s=0,x;
   fin>>n>>k;
   fin>>x;
   Q.push_back(make_pair(x,1));
   if(n==1)s+=x;
   for(i=2;i<=n;i++)
   {
       fin>>x;
       while(Q.empty()==0 && Q.front().first>x)Q.pop_back();
       Q.push_back(make_pair(x,i));
       if(Q.front().second<i-k+1)Q.pop_front();
       if(i>=k)s+=Q.front().first;
   }
   fout<<s;
}