import java.io.*;
import java.util.*;
public class TestClass {
	 public static void main(String[] args) { 
		      Scanner sc = new Scanner(System.in);
        int arraySize = sc.nextInt();
        int[]numArray = new int[arraySize];
        for(int i = 0;i<arraySize;i++){
            numArray[i] = sc.nextInt();
        }
       
        Arrays.sort(numArray);
        
        int count = 1;
        int currentToy=numArray[0];
        for(int i = 1;i<numArray.length;i++){
            if(numArray[i]>currentToy+4){
                count++;
                currentToy=numArray[i];
            }
        }
        System.out.println(count);
	}
}

• Problem Description
  Little Priyanka visited a kids’ shop. There are N toys and their weight is represented by an array W=[w1, w2,…,wN]. Each toy costs 1 unit, and if she buys a toy with weight w’, then she can get all other toys whose weight lies between [w’,w’+4] (both inclusive) free of cost. 
  
  Input Format:
  The first line contains an integer N i.e. number of toys.
  Next line will contain N integers,w1,w2,…,wN , representing the weight array.
  
  Output Format:
  Minimum units with which Priyanka could buy all of toys.
  
  Constraints
  1 <= N <= 10^5
  0 <= wi <= 10^4, where i belongs to [1,N]
• Test Case 1
  Input (stdin)5
  1 2 3 17 10
  Expected Output3
• Test Case 2
  Input (stdin)4
  1 2 3 17
  Expected Output2