Go: package main

import (
	"fmt"
	"sort"
	"strconv"
)

func main() {
	var v int
	for {
		fmt.Scan(&v)
		if v == 0 {
			break
		}
		if v%1111 == 0 {
			fmt.Println("NA")
			continue
		}
		count := 0
		for v != 6174 {
			str := ([]byte)(strconv.Itoa(v))
			sort.Slice(str, func(i, j int) bool {
				return str[i] < str[j]
			})
			s, _ := strconv.Atoi(string(str))
			sort.Slice(str, func(i, j int) bool {
				return str[i] > str[j]
			})
			l, _ := strconv.Atoi(string(str))
			v = l - s
			count++
		}
		fmt.Println(count)
	}
}

C++: #include <bits/stdc++.h>
using namespace std;

int s(int n, bool f) {
  vector<int> a;
  while (n) {
    a.push_back(n % 10);
    n /= 10;
  }

  sort(a.begin(), a.end());
  if (f) reverse(a.begin(), a.end());

  int res = 0;
  for (int i = 0; i < a.size(); ++i) {
    res *= 10;
    res += a[i];
  }

  return res;
}

int main() {
  int n;

  while (cin >> n, n) {
    if (n % 1111 == 0) {
      cout << "NA" << endl;
      continue;
    }

    int cnt = 0;
    while (n != 6174) {
      cnt++;
      n = s(n, true) - s(n, false);
    }

    cout << cnt << endl;
  }
}