#include<iostream>
#include<algorithm>
#include<string>
#include<cstdio>
#include<cstdlib>
#define rep(i,a) for( int i = 0; i != (a); ++i )

std::string intToStr( int n )
{
	char str[5];
	sprintf( str, "%04d", n );

	return str;
}

int main()
{
	std::string L, S;
	while( std::cin >> L, L != "0000" )
	{
		bool fl = true;

		rep( i, 3 )
			fl &= L[i+1] == L[i];
		if( fl )
		{
			std::cout << "NA" << std::endl;
			continue;
		}

		int ans = 0;
		while( L != "6174" )
		{
			S = L;
			std::sort( L.rbegin(), L.rend() );
			std::sort( S.begin(), S.end() );

			++ans;

			L = intToStr( atoi( L.c_str() ) - atoi( S.c_str() ) );
		}

		std::cout << ans << std::endl;
	}

	return 0;
}