#include <iostream>
#include <fstream>
#include <queue>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,a[5000005],q[5000005],pos[5000005],st=1,dr=0;
long long sol=0;
int main()
{ int i;
    f>>n>>k;
  for(i=1;i<=n;i++)
  { f>>a[i];
      while(dr>=st && a[i]<q[dr]) dr--;
    dr++; q[dr]=a[i]; pos[dr]=i;
      while(pos[st]<=i-k) st++;
      if (i>=k) sol+=q[st];
  }
  g<<1LL*sol;
    return 0;
}