Given a 4-digit positive integer with different digits, if we first rank the 4 digits in non increasing order, then rank them in non decreasing order, and then subtract the second digit from the first digit, we will get a new digit. We will soon stop at 6174, the "digital black hole", which is also called Kaprekar constant.

For example, starting with 6767, we will get

7766 - 6677 = 1089
9810 - 0189 = 9621
9621 - 1269 = 8352
8532 - 2358 = 6174
7641 - 1467 = 6174
... ...
Given any 4-bit positive integer, please write a program to demonstrate the process of reaching the black hole.

Input format:
Enter to give a (0,10
​4
The positive integer N in the interval.

Output format:
If the four digits of N are all equal, output N - N = 0000 in one line; otherwise, output each step of calculation in one line until 6174 appears as a difference. See the example for the output format. Note that each number is output in 4-digit format.

Enter example 1:
6767
Output example 1:
7766 - 6677 = 1089
9810 - 0189 = 9621
9621 - 1269 = 8352
8532 - 2358 = 6174
Enter example 2:
2222
Output example 2:
2222 - 2222 = 0000

Note the processing of 0 when calculating and outputting.

#include<iostream>
#include<string>
#include <sstream>
#include <iomanip>
using namespace std;
void check(string& str)
{
	switch (str.size())
	{
	case 1:
		str = "000" + str;
		break;
	case 2:
		str = "00" + str;
		break;
	case 3:
		str = "0" + str;
		break;
	default:
		break;
	}
}
int func(int a)
{
	int result;
	string str = to_string(a);
	check(str);
	string b = "";
	for (int i = str.size() - 1; i >= 0; i--)
		b += str[i];
	stringstream ss;
	ss << b;
	ss >> result;
	return result;
}
int sort(int a)
{

	int result;
	string str = to_string(a);
	check(str);
	for (int i = 0; i < str.size() - 1; i++)
		for (int j = i + 1; j < str.size(); j++)
		{
			if (str[j] > str[i])
			{
				int tmp = str[j];
				str[j] = str[i];
				str[i] = tmp;
			}
		}
	stringstream ss;
	ss << str;
	ss >> result;
	return result;
}
void print(int n)
{
	int a, b;
	do
	{
		a = sort(n);
		b = func(a);
		if (a - b == 0)
		{
			cout << setw(4) << setfill('0') << a << " - " << setw(4) << setfill('0') << b << " = " << setw(4) << setfill('0') << (a - b) << endl;
			break;
		}
		cout << setw(4) << setfill('0') << a << " - " << setw(4) << setfill('0') << b << " = " << setw(4) << setfill('0') << (a - b) << endl;
		n = a - b;
	} while ((a - b) != 6174);
}
int main()
{
	int n;
	cin >> n;
	print(n);
	return 0;
}