#include <fstream>
#include <deque>
using namespace std;
ifstream fi("deque.in");
ofstream fo("deque.out");
int n,k,i,a[5000000];
long long sol;
deque<int> d;

int main()
{fi>>n>>k;
 for(i=1;i<=n;i++) fi>>a[i];

for(i=1;i<=n;i++)
 {
  while(!d.empty() and a[d.back()]>=a[i]) d.pop_back();
  while(!d.empty() and d.front() < i-k+1) d.pop_front();
  d.push_back(i);
  if(i>=k)  sol+=a[d.front()];
 }
fo<<sol;
    return 0;
}