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 <iostream>
#include <string>
#include <algorithm>
#include <deque>
using namespace std;
string L(string);
string S(string);
string sa(string,string);
int main(void)
{
	int count;
	string n;

	while(1){
		cin >> n;
		if(n=="0000") break;
		if(n=="1111"||n=="2222"||n=="3333"||n=="4444"||n=="5555"||n=="6666"||n=="7777"||n=="8888"||n=="9999") {
			cout << "NA" << endl;
			continue;
		}
		count=0;
		while(n!="6174"){
			n=sa(L(n),S(n));
			count+=1;
		}
		cout << count << endl;
	}
	return 0;
}
string S(string n)
{
	string s;
	deque<char> dn;
	for(int i=0;i<4;i++) dn.push_back(n[i]);
	sort(dn.begin(),dn.end());
	for(int i=3;0<=i;i--){
		s+=dn[i];
		dn.pop_back();
	}
	return s;
}
string L(string n)
{
	string l;
	deque<char> dn;
	for(int i=0;i<4;i++) dn.push_back(n[i]);
	sort(dn.begin(),dn.end());
	for(int i=0;i<4;i++){
		l+=dn[i];
	}
	return l;
}
string sa(string l,string s)
{
	string n;
	int lnum=0,snum=0,num,b=1;
	for(int i=3;0<=i;i--){
		lnum+=(b*(l[3-i]-'0'));
		snum+=(b*(s[3-i]-'0'));
		b*=10;
	}
	num=lnum-snum;
	for(int i=0;i<4;i++){
		b/=10;
		n+=((num/b)%10+'0');
	}
	cout << n << endl;
	return n;
}

C++: #include<iostream>
#include<algorithm>
#include<functional>
#include<cstring>

int main() {
	int n;
	bool used[10000];
	while (std::cin >> n) {
		int str[4] = { (n / 1000),(n / 100) % 10,(n / 10) % 10,n % 10 };
		if (n % 1111 == 0) {
			if (str[0] == 0)
				break;
			else
				std::cout << "NA" << std::endl;

		}
		std::memset(used, false, sizeof(used));
		used[n] = true;
		int cnt = 0;
		while(n!=6174) {
			++cnt;
			std::sort(str, str + 4, std::greater<int>());
			int l = str[0] * 1000 + str[1] * 100 + str[2] * 10 + str[3];
			std::sort(str, str + 4);
			int	s = str[0] * 1000 + str[1] * 100 + str[2] * 10 + str[3];
			n = l - s;
			if (used[n])
				goto a;
			used[n] = true;
			str[0] = n / 1000;
			str[1] = (n / 100) % 10;
			str[2] = (n / 10) % 10;
			str[3] = n % 10;
		}
		std::cout << cnt << std::endl;
	a:;
	}
	return 0;
}

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

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef set<int> si;
typedef set<ll, ll> sll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef map<int, int> mii;
typedef map<int, ll> mil;
typedef map<ll, int> mli;
typedef map<ll, ll> mll;

#define FOR(i, a, b) for(int i = (a), loop_end_##i=(b); i < (loop_end_##i); i++)
#define REP(i, n) FOR(i, 0, n)
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define SORT(c) sort((c).begin(),(c).end())
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define PB push_back

#define dump(x)  cout << #x << " = " << (x) << endl
#define debug(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl

#define rep(v,n) for(int v=0;v<n;v++)
#define input(t,v) t v;cin>>v;
#define input2(t,v1,v2) t v1,v2;cin>>v1>>v2;
#define input3(t,v1,v2,v3) t v1,v2,v3;cin>>v1>>v2>>v3;

template<class T> T read() {
	T t;
	cin >> t;
	return t;
}

int main(){
	while(true){
		input(int,n);
		if(n==0)return 0;
		if(n%1111==0){cout<<"NA"<<endl;continue;}
		int ret=0;
		while(n!=6174){
			int ds[4],tmp;
			tmp=n;
			rep(i,4){
				ds[i]=tmp%10;
				tmp/=10;
			}
			sort(begin(ds),end(ds));
			
			int S=ds[0]*1000+ds[1]*100+ds[2]*10+ds[3];
			int L=ds[3]*1000+ds[2]*100+ds[1]*10+ds[0];
			n=L-S;
			ret++;
		}
		cout<<ret<<endl;
	}
	
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
using namespace std;
int main() {
	char S[5];
	while(scanf("%s",S)) {
		if(strcmp(S,"0000")==0) break;
		int ans=0;
		bool NG=0;
		while(strcmp(S,"6174")) {
			sort(S,S+4);
			NG=1;
			for(int i=0;i<3;i++) {
				if(S[i]!=S[i+1]) NG=0;
			}
			if(NG) break;
			int a=0,b=0,c=1;
			for(int i=0;i<4;i++) {
				a+=(S[i]-'0')*c;
				b+=(S[3-i]-'0')*c;
				c*=10;
			}
			int k=a-b;
			for(int i=3;i>=0;i--) {
				S[i]=(k%10+'0');
				k/=10;
			}
			ans++;
		}
		if(NG) printf("NA\n"); else printf("%d\n",ans);
	}
}

C++: #include <cassert>

#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
//#include <boost/foreach.hpp>
//#include <boost/range/algorithm.hpp>
#define rep(i,j,k) for(int i=(int)j;i<(int)k;i++)
#define ll long long
#define Sort(v) sort(all(v))
#define INF 1e9
#define LINF 1e18
#define END return 0
#define pb push_back
#define se second
#define fi first
#define pb push_back
#define all(v) (v).begin() , (v).end()
#define MP make_pair
#define MOD 1000000007LL
#define int long long
using namespace std;
int day[12]={31,28,31,30,31,30,31,31,30,31,30,31};
int dx[]={0,1,0,-1};
int dy[]={1,0,-1,0};
struct edge{int to,cost;};
//typedef pair<int,int> P;

bool isupper(char c){if('A'<=c&&c<='Z')return 1;return 0;}
bool islower(char c){if('a'<=c&&c<='z')return 1;return 0;}
bool isPrime(int x){if(x==1)return 0;if(x==2)return 1;if(x%2==0)return 0;for(int i=3;i*i<=x;i++)if(x%i==0)return 0;return 1;}
bool iskaibun(string s){for(int i=0;i<s.size()/2;i++)if(s[i]!=s[s.size()-i-1])return 0;return 1;}
bool isnumber(char c){return ('0'<=c&&c<='9');}
bool isalpha(char c){return (isupper(c)&&islower(c));}
void printvi(vector<int> v){rep(i,0,v.size()){if(i)cout<<" ";cout<<v[i];}cout<<endl;}
void printvil(vector<int> v){rep(i,0,v.size()){cout<<v[i]<<endl;}}
void printvvi(vector<vector<int>> v){
    rep(i,0,v.size()){
        rep(j,0,v[i].size()){
            if(j)cout<<" ";
            cout<<v[i][j];
        }
        cout<<endl;
    }
}
void printvstr(vector<string> v){
    rep(i,0,v.size()){
        cout<<v[i]<<endl;
    }
}

signed main (){
    string s;
    while(1){
        cin>>s;
        if(s=="0000")break;
        auto cmp=[&](char a,char b){
            return a>b;
        };
        if(s[0]==s[1] and s[1]==s[2] and s[2]==s[3]){
            cout<<"NA"<<endl;
            continue;
        }
        int i=0;
        for(;s!="6174";i++){
            sort(all(s));
            int a1=stol(s);
            sort(all(s),cmp);
            int a2=stol(s);
            int a3=a2-a1;
            s=to_string(a3);
        }
        cout<<i<<endl;

    }

    
}
/*
*/