#include <bits/stdc++.h>
#define int long long
using namespace std;

deque<int>q;
int v[5000005];

signed main()
{
  ifstream cin("deque.in");
ofstream cout("deque.out");
    int n,k,a,sum=0;
    cin>>n>>k;
    for(int i=0;i<k;i++)
    {
      cin>>v[i];
      while(!q.empty() && v[q.back()]>v[i])
        q.pop_back();
      q.push_back(i);
    }
    sum+=v[q.front()];
   for(int i=k;i<n;i++)
    {
      cin>>v[i];
      if(q.front()<=i-k)
        q.pop_front();
      while(!q.empty() && v[q.back()]>v[i])
        q.pop_back();
      q.push_back(i);
     // cout<<q.front()<<endl;
      sum+=v[q.front()];
    }
    cout<<sum;
    return 0;
}