#include <iostream>
#include <vector>
 
int main() {
	static int UPPER_LIMIT = 10001;
	static int K = 32;
	int frequencies[UPPER_LIMIT] = {0}; // O(U)
	int n;
	std::cin >> n;
	for (int i = 0; i < n; i++) { // O(n)
	 int x;
	 std::cin >> x;
	 frequencies[x] += 1;
	}
	for (int i = 1; i < UPPER_LIMIT; i++) { // O(U)
		frequencies[i] += frequencies[i-1];
	}
	int count = 0;
	for (int i = 1; i < UPPER_LIMIT; i++) { // O(U)
	  int low_idx = std::max(i-32, 0);
	  int number_of_elements_with_value_i = frequencies[i] - frequencies[i-1];
	  if (number_of_elements_with_value_i == 0) continue;
	  int number_of_elements_with_value_K_close_to_i =
	      (frequencies[i] - frequencies[low_idx]) - 1; // to avoid adding number
	                                                   // with itself. 
      std::cout << "i: " << i << " number_of_elements_with_value_i: " << number_of_elements_with_value_i << " number_of_elements_with_value_K_close_to_i: " << number_of_elements_with_value_K_close_to_i << std::endl;
	  count += number_of_elements_with_value_i * number_of_elements_with_value_K_close_to_i;
	}
	std::cout << count;
	return 0;
}

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