#include <iostream>
#include <fstream>
#define ll long long
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
 int n,k,a[5000005],v[5000005],st,dr;
 ll sol;
int main()
{ int i,j,x;
    f>>n>>k;
     st=1; dr=0;

    for(i=1;i<=n;i++)
    { f>>v[i];

      while(st<=dr && v[i]<=v[a[dr]])
       dr--;

      while(st<=dr && a[st]<i-k+1)
       st++;





      dr++; a[dr]=i;

         if (i>=k) sol+=v[a[st]];

    }
    g<<sol<<"\n";
    return 0;
}