Problem p00254 (C++) — buggy submission, verdict: Runtime Error

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

#define in ,
#define esc_paren(...) __VA_ARGS__
#define pp_empty(...)
#define pp_cat_i(x, y) x##y
#define pp_cat(x, y) pp_cat_i(x, y)

#define pp_inc0 1
#define pp_inc1 2
#define pp_inc2 3
#define pp_inc3 4
#define pp_inc4 5
#define pp_inc5 6
#define pp_inc6 7
#define pp_inc7 8
#define pp_inc8 9
#define pp_inc(i) pp_cat(pp_inc, i)

#define pp_arg10(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, ...) _9
#define pp_has_comma(...) pp_arg10(__VA_ARGS__, 1, 1, 1, 1, 1, 1, 1, 1, 0)
#define pp_trigger_paren(...) ,
#define pp_is_empty(...)                                                       \\
  pp_is_empty1(pp_has_comma(__VA_ARGS__),                                      \\
               pp_has_comma(pp_trigger_paren __VA_ARGS__),                     \\
               pp_has_comma(__VA_ARGS__()),                                    \\
               pp_has_comma(pp_trigger_paren __VA_ARGS__()))
#define pp_paste5(_0, _1, _2, _3, _4) _0##_1##_2##_3##_4
#define pp_is_empty1(_0, _1, _2, _3)                                           \\
  pp_has_comma(pp_paste5(pp_is_empty_case_, _0, _1, _2, _3))
#define pp_is_empty_case_0001 ,

#define pp_is_one(...) pp_is_one_(__VA_ARGS__, pp_one_seq)
#define pp_is_one_(...) pp_is_one_n(__VA_ARGS__)
#define pp_is_one_n(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, N, ...) N
#define pp_one_seq 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0

#define pp_narg(...) pp_narg_(__VA_ARGS__, pp_narg_seq)
#define pp_narg_(...) pp_narg_n(__VA_ARGS__)
#define pp_narg_n(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, \\
                  _15, _16, _17, _18, _19, _20, _21, _22, _23, _24, _25, _26,  \\
                  _27, _28, _29, _30, _31, _32, _33, _34, _35, _36, _37, _38,  \\
                  _39, _40, _41, _42, _43, _44, _45, _46, _47, _48, _49, _50,  \\
                  _51, _52, _53, _54, _55, _56, _57, _58, _59, _60, _61, _62,  \\
                  _63, n, ...)                                                 \\
  n
#define pp_narg_seq                                                            \\
  63, 62, 61, 60, 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, 45,  \\
      44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27,  \\
      26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9,   \\
      8, 7, 6, 5, 4, 3, 2, 1, 0

#define pp_if_0(x, y) y
#define pp_if_1(x, y) x
#define pp_if(cond, x, y) pp_cat(pp_if_, cond)(x, y)

#define pp_foreach_i9(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i8(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i7(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i6(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i5(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i4(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i3(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i2(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i1(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i0(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i(i, f, ...)                                                \\
  pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                                    \\
        pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach(f, ...) pp_foreach_i(0, f, __VA_ARGS__)

typedef long long ll;
#define down_queue(x) priority_queue<x>
#define up_queue(x) priority_queue<x, vector<x>, greater<x>>
#define all(x) x.begin(), x.end()
#define split_str(str, sp_word)                                                \\
  istringstream stream(str);                                                   \\
  string res;                                                                  \\
  for (int cnt = 0; getline(stream, res, sp_word); cnt++)
#define digit(x) ((int)log10((double)(x)) + 1)
#define mp(x, y) make_pair(x, y)
#define pb(x) push_back(x)
#define pf(x) push_front(x)
#define vec_cpy(to, from) copy(all(to), back_inserter(from))
#define ary_cpy(to, from) memcpy(to, from, sizeof(from))
#define MOD 1000000007
#define INF 999999999

#define rep(...) rep1(rep2, (__VA_ARGS__))
#define rep1(X, A) X A
#define rep2(i, ...)                                                           \\
  pp_if(pp_is_one(__VA_ARGS__), rep_len1(i, __VA_ARGS__), rep3(i, __VA_ARGS__))
#define rep_len1(i, end, ...) for (int i = 0; i < end; i++)
#define rep3(i, iter, ...) rep4(rep5, (iter, i, esc_paren __VA_ARGS__))
#define rep4(X, A) X A
#define rep5(iter, ...) iter(__VA_ARGS__)

#define up up_iter,
#define up_iter3(i, start, end) for (int i = start; i < end; i++)
#define up_iter4(i, start, end, up) for (int i = start; i < end; i += up)
#define up_iter(...) pp_cat(up_iter, pp_narg(__VA_ARGS__))(__VA_ARGS__)
#define down down_iter,
#define down_iter2(i, end) for (int i = end - 1; i >= 0; i--)
#define down_iter3(i, start, end) for (int i = end - 1; i >= start; i--)
#define down_iter4(i, start, end, down)                                        \\
  for (int i = end - 1; i >= start; i -= down)
#define down_iter(...) pp_cat(down_iter, pp_narg(__VA_ARGS__))(__VA_ARGS__)
#define viter viter_iter,
#define viter_iter(i, v)                                                       \\
  auto tmpitr = v.begin();                                                     \\
  for (auto i = *tmpitr; tmpitr != v.end(); tmpitr++)

#define debug_var_elem(v) << #v << "=" << v << " "
#ifdef DEBUG
#define debug_echo(e) cout << "L" << __LINE__ << ": " << e << endl
#define debug_var(...)                                                         \\
  cout << "L" << __LINE__ << ": " pp_foreach(debug_var_elem, __VA_ARGS__)      \\
       << endl
#else
#define debug_echo(e)
#define debug_var(...)
#endif

#define pp_gen_field(list) pp_gen_field1 list
#define pp_gen_field1(name, val) decltype(val) name;
#define pp_gen_init(list) pp_gen_init1 list
#define pp_gen_init1(name, val) , val
#define pp_gen_find_set_wrap(ufnodename) ufnodename pp_gen_find_set
#define pp_gen_find_set(list) pp_gen_find_set1 list
#define pp_gen_find_set1(name, val)                                            \\
  find_set_##name(int x, decltype(val) v) {                                    \\
    if (nodes[x].parent == x) {                                                \\
      nodes[x].name = v;                                                       \\
      return nodes[x];                                                         \\
    } else {                                                                   \\
      return nodes[x] = find_set_##name(nodes[x].parent, v);                   \\
    }                                                                          \\
  }
#define pp_gen_unite_set(list) pp_gen_unite_set1 list
#define pp_gen_unite_set1(name, val)                                           \\
  if (nodes[x].name == val) {                                                  \\
    find_set_##name(x, find(y).name);                                          \\
  }                                                                            \\
  if (nodes[y].name == val) {                                                  \\
    find_set_##name(y, find(x).name);                                          \\
  }

#define def_unionfind(ufname, ufnodename, ...)                                 \\
  struct ufnodename {                                                          \\
    int parent;                                                                \\
    pp_foreach(pp_gen_field, __VA_ARGS__)                                      \\
  };                                                                           \\
  struct ufname {                                                              \\
    vector<ufnodename> nodes;                                                  \\
    vector<int> rank;                                                          \\
    ufname(int n) : nodes(n + 1), rank(n + 1) {                                \\
      rep(i in n) {                                                            \\
        nodes[i] = ufnodename{i pp_foreach(pp_gen_init, __VA_ARGS__)};         \\
        rank[i] = 0;                                                           \\
      }                                                                        \\
    }                                                                          \\
    ufnodename find(int x) {                                                   \\
      if (nodes[x].parent == x) {                                              \\
        return nodes[x];                                                       \\
      } else {                                                                 \\
        return nodes[x] = find(nodes[x].parent);                               \\
      }                                                                        \\
    }                                                                          \\
    pp_foreach(pp_gen_find_set_wrap(ufnodename),                               \\
               __VA_ARGS__) void unite(int x, int y) {                         \\
      x = find(x).parent;                                                      \\
      y = find(y).parent;                                                      \\
      if (x == y)                                                              \\
        return;                                                                \\
      if (rank[x] < rank[y]) {                                                 \\
        pp_foreach(pp_gen_unite_set, __VA_ARGS__);                             \\
        nodes[x].parent = y;                                                   \\
      } else {                                                                 \\
        pp_foreach(pp_gen_unite_set, __VA_ARGS__);                             \\
        nodes[y].parent = x;                                                   \\
        if (rank[x] == rank[y])                                                \\
          rank[x]++;                                                           \\
      }                                                                        \\
    }                                                                          \\
    bool same(int x, int y) { return find(x).parent == find(y).parent; }       \\
  }

ll gcd(ll a, ll b) {
  while (b) {
    ll tmp = a % b;
    a = b;
    b = tmp;
  }
  return a;
}
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }

#define def_varargs(name, f)                                                   \\
  template <typename First> inline First name(First first) { return first; }   \\
  template <typename First, typename... Rest>                                  \\
  inline First name(First first, Rest... rest) {                               \\
    return f(first, name(rest...));                                            \\
  }

int ans = 0;

template <typename T> string tostr(const T &t) {
  ostringstream os;
  os << t;
  return os.str();
}

void oper(string num, int cnt) {
  string buff;

  if (stoi(num) == 6174) {
    ans = cnt;
    return;
  }

  sort(all(num));
  buff = num;
  reverse(all(buff));

  if (buff.size() != 4)
    rep(_ in 4 - (int)buff.size()) buff += '0';

  int diff = stoi(buff) - stoi(num);
  debug_var(stoi(buff) - stoi(num), num, buff, diff);
  oper(tostr(diff), cnt + 1);
}

int main() {
  string n;
  while (cin >> n) {
    if (n[0] == n[1] && n[0] == n[2] && n[0] == n[3]) {
      if (stoi(n) == 0)
        return 0;
      cout << "NA" << endl;
    } else {
      oper(n, 0);
      cout << ans << endl;
    }
  }
}

Error: 0

Fixed submission:

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

// pp basics

#define in ,
#define esc_paren(...) __VA_ARGS__
#define pp_empty(...)
#define pp_cat_i(x, y) x##y
#define pp_cat(x, y) pp_cat_i(x, y)

#define pp_inc0 1
#define pp_inc1 2
#define pp_inc2 3
#define pp_inc3 4
#define pp_inc4 5
#define pp_inc5 6
#define pp_inc6 7
#define pp_inc7 8
#define pp_inc8 9
#define pp_inc(i) pp_cat(pp_inc, i)

// pp args counter

#define pp_arg10(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, ...) _9
#define pp_has_comma(...) pp_arg10(__VA_ARGS__, 1, 1, 1, 1, 1, 1, 1, 1, 0)
#define pp_trigger_paren(...) ,
#define pp_is_empty(...)                                                       \\
  pp_is_empty1(pp_has_comma(__VA_ARGS__),                                      \\
               pp_has_comma(pp_trigger_paren __VA_ARGS__),                     \\
               pp_has_comma(__VA_ARGS__()),                                    \\
               pp_has_comma(pp_trigger_paren __VA_ARGS__()))
#define pp_paste5(_0, _1, _2, _3, _4) _0##_1##_2##_3##_4
#define pp_is_empty1(_0, _1, _2, _3)                                           \\
  pp_has_comma(pp_paste5(pp_is_empty_case_, _0, _1, _2, _3))
#define pp_is_empty_case_0001 ,

#define pp_is_one(...) pp_is_one_(__VA_ARGS__, pp_one_seq)
#define pp_is_one_(...) pp_is_one_n(__VA_ARGS__)
#define pp_is_one_n(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, N, ...) N
#define pp_one_seq 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0

#define pp_narg(...) pp_narg_(__VA_ARGS__, pp_narg_seq)
#define pp_narg_(...) pp_narg_n(__VA_ARGS__)
#define pp_narg_n(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, \\
                  _15, _16, _17, _18, _19, _20, _21, _22, _23, _24, _25, _26,  \\
                  _27, _28, _29, _30, _31, _32, _33, _34, _35, _36, _37, _38,  \\
                  _39, _40, _41, _42, _43, _44, _45, _46, _47, _48, _49, _50,  \\
                  _51, _52, _53, _54, _55, _56, _57, _58, _59, _60, _61, _62,  \\
                  _63, n, ...)                                                 \\
  n
#define pp_narg_seq                                                            \\
  63, 62, 61, 60, 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, 45,  \\
      44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27,  \\
      26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9,   \\
      8, 7, 6, 5, 4, 3, 2, 1, 0

// pp if
#define pp_if_0(x, y) y
#define pp_if_1(x, y) x
#define pp_if(cond, x, y) pp_cat(pp_if_, cond)(x, y)

// pp foreach
#define pp_foreach_i9(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i8(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i7(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i6(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i5(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i4(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i3(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i2(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i1(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i0(i, f, x, ...)                                            \\
  f(x) pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                               \\
             pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach_i(i, f, ...)                                                \\
  pp_if(pp_is_empty(__VA_ARGS__), pp_empty,                                    \\
        pp_cat(pp_foreach_i, i))(pp_inc(i), f, __VA_ARGS__)
#define pp_foreach(f, ...) pp_foreach_i(0, f, __VA_ARGS__)

// alternative rep macro
#define rep(...) rep1(rep2, (__VA_ARGS__))
#define rep1(X, A) X A
#define rep2(i, ...)                                                           \\
  pp_if(pp_is_one(__VA_ARGS__), rep_len1(i, __VA_ARGS__), rep3(i, __VA_ARGS__))
#define rep_len1(i, end, ...) for (int i = 0; i < end; i++)
#define rep3(i, iter, ...) rep4(rep5, (iter, i, esc_paren __VA_ARGS__))
#define rep4(X, A) X A
#define rep5(iter, ...) iter(__VA_ARGS__)

// iterators
#define up up_iter,
#define up_iter3(i, start, end) for (int i = start; i < end; i++)
#define up_iter4(i, start, end, up) for (int i = start; i < end; i += up)
#define up_iter(...) pp_cat(up_iter, pp_narg(__VA_ARGS__))(__VA_ARGS__)
#define down down_iter,
#define down_iter2(i, end) for (int i = end - 1; i >= 0; i--)
#define down_iter3(i, start, end) for (int i = end - 1; i >= start; i--)
#define down_iter4(i, start, end, down)                                        \\
  for (int i = end - 1; i >= start; i -= down)
#define down_iter(...) pp_cat(down_iter, pp_narg(__VA_ARGS__))(__VA_ARGS__)
#define viter viter_iter,
#define viter_iter(i, v)                                                       \\
  auto tmpitr = v.begin();                                                     \\
  for (auto i = *tmpitr; tmpitr != v.end(); tmpitr++)

// debug macros
#define debug_var_elem(v) << #v << "=" << v << " "
#ifdef DEBUG
#define debug_echo(e) cout << "L" << __LINE__ << ": " << e << endl
#define debug_var(...)                                                         \\
  cout << "L" << __LINE__ << ": " pp_foreach(debug_var_elem, __VA_ARGS__)      \\
       << endl
#define debug_ary(ary, n)                                                      \\
  cout << "L" << __LINE__ << " [ ";                                            \\
  for (int i = 0; i < n; i++)                                                  \\
    cout << ary[i] << " ";                                                     \\
  cout << "]" << endl;
#else
#define debug_echo(e)
#define debug_var(...)
#define debug_ary(ary, n)
#endif

// short names
typedef long long ll;
#define down_queue(x) priority_queue<x>
#define up_queue(x) priority_queue<x, vector<x>, greater<x>>
ll gcd(ll a, ll b) {
  while (b) {
    ll tmp = a % b;
    a = b;
    b = tmp;
  }
  return a;
}
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
#define all(x) x.begin(), x.end()
#define split_str(str, sp_word)                                                \\
  istringstream stream(str);                                                   \\
  string res;                                                                  \\
  for (int cnt = 0; getline(stream, res, sp_word); cnt++)
#define digit(x) ((int)log10((double)(x)) + 1)
#define mp(x, y) make_pair(x, y)
#define pb(x) push_back(x)
#define pf(x) push_front(x)
#define vec_cpy(to, from) copy(all(to), back_inserter(from))
#define ary_cpy(to, from) memcpy(to, from, sizeof(from))
#define MOD 1000000007

// pp unionfind

#define pp_gen_field(list) pp_gen_field1 list
#define pp_gen_field1(name, val) decltype(val) name;
#define pp_gen_init(list) pp_gen_init1 list
#define pp_gen_init1(name, val) , val
#define pp_gen_find_set_wrap(ufnodename) ufnodename pp_gen_find_set
#define pp_gen_find_set(list) pp_gen_find_set1 list
#define pp_gen_find_set1(name, val)                                            \\
  find_set_##name(int x, decltype(val) v) {                                    \\
    if (nodes[x].parent == x) {                                                \\
      nodes[x].name = v;                                                       \\
      return nodes[x];                                                         \\
    } else {                                                                   \\
      return nodes[x] = find_set_##name(nodes[x].parent, v);                   \\
    }                                                                          \\
  }
#define pp_gen_unite_set(list) pp_gen_unite_set1 list
#define pp_gen_unite_set1(name, val)                                           \\
  if (nodes[x].name == val) {                                                  \\
    find_set_##name(x, find(y).name);                                          \\
  }                                                                            \\
  if (nodes[y].name == val) {                                                  \\
    find_set_##name(y, find(x).name);                                          \\
  }

#define def_unionfind(ufname, ufnodename, ...)                                 \\
  struct ufnodename {                                                          \\
    int parent;                                                                \\
    pp_foreach(pp_gen_field, __VA_ARGS__)                                      \\
  };                                                                           \\
  struct ufname {                                                              \\
    vector<ufnodename> nodes;                                                  \\
    vector<int> rank;                                                          \\
    ufname(int n) : nodes(n + 1), rank(n + 1) {                                \\
      rep(i in n) {                                                            \\
        nodes[i] = ufnodename{i pp_foreach(pp_gen_init, __VA_ARGS__)};         \\
        rank[i] = 0;                                                           \\
      }                                                                        \\
    }                                                                          \\
    ufnodename find(int x) {                                                   \\
      if (nodes[x].parent == x) {                                              \\
        return nodes[x];                                                       \\
      } else {                                                                 \\
        return nodes[x] = find(nodes[x].parent);                               \\
      }                                                                        \\
    }                                                                          \\
    pp_foreach(pp_gen_find_set_wrap(ufnodename),                               \\
               __VA_ARGS__) void unite(int x, int y) {                         \\
      x = find(x).parent;                                                      \\
      y = find(y).parent;                                                      \\
      if (x == y)                                                              \\
        return;                                                                \\
      if (rank[x] < rank[y]) {                                                 \\
        pp_foreach(pp_gen_unite_set, __VA_ARGS__);                             \\
        nodes[x].parent = y;                                                   \\
      } else {                                                                 \\
        pp_foreach(pp_gen_unite_set, __VA_ARGS__);                             \\
        nodes[y].parent = x;                                                   \\
        if (rank[x] == rank[y])                                                \\
          rank[x]++;                                                           \\
      }                                                                        \\
    }                                                                          \\
    bool same(int x, int y) { return find(x).parent == find(y).parent; }       \\
  }

int ans = 0;

template <typename T> string tostr(const T &t) {
  ostringstream os;
  os << t;
  return os.str();
}

void oper(string num, int cnt) {
  string buff;

  if (stoi(num) == 6174) {
    ans = cnt;
    return;
  }

  sort(all(num));
  buff = num;
  reverse(all(buff));
  int diff = stoi(buff) - stoi(num);
  oper(tostr(diff), cnt + 1);
}

int main() {
  string n;
  bool flag;
  while (cin >> n) {
    if (stoi(n) == 0)
      return 0;
    flag = true;

    rep(i in up(0, n.length())) if (n[0] != n[i]) flag = false;

    if (flag) {
      cout << "NA" << endl;
    } else {
      oper(n, 0);
      cout << ans << endl;
    }
  }
}