#include <iostream>
using namespace std;
 
// A utility function to find minimum of
// 3 elements
int minimum(long long int* a, int b, int c)
{
   long long  int min=a[b];
    for(int i=b;i<=c;i++)
    	if(a[i]<min)
    	min=a[i];
    	
    	return min;
}
 
// Returns minimum possible sum of elements such
// that an element out of every three consecutive
// elements is picked.
int findMinSum(long long int *arr, int n,int k)
{
    // Create a DP table to store results of
    // subpriblems. sum[i] is going to store
    // minimum possible sum when arr[i] is
    // part of the solution.
    long long int sum[n];
 
    // When there are less than or equal to
    // 3 elements
    for(int i=0;i<k;i++)
    
    sum[i] = arr[i];
 
    // Iterate through all other elements
    for (int i=k; i<n; i++)
      sum[i] = arr[i] +
              minimum(sum,i-k,i);
 
    return minimum(sum,n-k,n-1);
}
 
// Driver code
int main()
{
    int n,k;
    cin >>n;
    cin >>k;
    long long int arr[n];
    for(int i=0;i<n;i++)
    cin>> arr[i];
    cout << findMinSum(arr, n,k+1);
    return 0;
}