#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque <int> d;
int i,n,k,a[5000001];
long long s;
int main()
{
    f>>n>>k;
     for(i=1;i<=n;i++)
      {        f>>a[i];
       while(!d.empty()&&d.back()>a[i])d.pop_back();
       d.push_back(a[i]);

          if(i>k&&d.front()==a[i-k])
          d.pop_front();

           if (i>=k)s+=d.front();    }    g<<s;


}