#include <iostream>
#include <fstream>
using namespace std;
#define max 5000000
#define minimum 10000001
int mins=minimum;
int v[max];
int main(){
  ifstream fin("deque.in");
  ofstream fout("deque.out");
  int A,K,i;
  long long int s=0,k;
  fin>>A>>K;
  k=K;
  for(i=1;i<=A;i++){
    fin>>v[i];}
  for(i=1;i<=A;i++){
    if(v[i]<mins)
      mins=v[i];
    if(i==k){
      s+=mins;
      mins=10000001;
      i=i-K+1;
      k++;
    }
  }
  fout<<s;
  return 0;
}