#include <iostream>
#include <fstream>
using namespace std;

int main(){
  ifstream fin("deque.in");
  ofstream fout("deque.out");
  int A,K,i;
  long long int nr,min=10000001,s=0,k,v[5000000];
  fin>>A>>K;
  k=K;
  for(i=1;i<=A;i++){
    fin>>v[i];}
  for(i=1;i<=A;i++){
    if(v[i]<min)
      min=v[i];
    if(i==k){
      s+=min;
      min=10000001;
      i=i-K+1;
      k++;
    }
  }
  fout<<s;
  return 0;
}