source_code: import java.util.*;
  import java.io.*;
  import java.util.Map.Entry;
  
  public class Codeforces {
  
      static int n;
      static double max;
      static int[] pre;
  
      public static void findIntensity(int l){
          for(int i = 0, j = i + l; j < n + 1; i++, j++){
              double res = (pre[j] - pre[i]) / (double) l;
              max = Math.max(max, res);
          }
      }
  
      public static void main(String[] args) throws IOException {
          BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
          StringTokenizer st = new StringTokenizer(br.readLine());
          n = Integer.parseInt(st.nextToken());
          int k = Integer.parseInt(st.nextToken());
          int[] heat = new int[n];
          st = new StringTokenizer(br.readLine());
          for(int i = 0; i < n; i++){
              heat[i] = Integer.parseInt(st.nextToken());
          }
          max = 0;
          pre = new int[n + 1];
          pre[0] = 0;
          for(int i = 0; i < n; i++){
              pre[i + 1] = pre[i] + heat[i];
          }
          for(int i = k; i <= n; i++){
              findIntensity(i);
          }
          System.out.println(max);
      }
  }