#include<fstream>
#include<deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
 
deque <int> q;
 
int a[5000004],n,k;
long long s=0;
 
int main(){
    f>>n>>k;
    for(int register i=1;i<=n;i++)
      {
       f>>a[i]; 
       while(q.size() && a[q.back()]>=a[i])q.pop_back();
       q.push_back(i);
       if(i>=k) s+=a[q.front()];
       if(q.front()==i-k+1) q.pop_front();
      }
     
    g<<s;
    f.close();
    g.close();
    return 0;
}