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

int w[100000];

int main()
{
	int n;
	cin >> n;
	for (int i = 0; i < n; i++)
		cin >> w[i];
	sort(w, w + n);
	int ans = 1, prev = w[0];
	for (int i = 1; i < n; i++)
		if (w[i] - prev > 4)
			prev = w[i], ans++;
	cout << ans << endl;
	return 0;
}

• 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