#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <ctime>
#include <cassert>
#include <iostream>
#include <cctype>
#include <sstream>
#include <string>
#include <list>
#include <vector>
#include <queue>
#include <set>
#include <stack>
#include <map>
#include <utility>
#include <numeric>
#include <algorithm>
#include <iterator>
#include <bitset>
#include <complex>
#include <fstream>
using namespace std;
typedef long long ll;
const double EPS = 1e-9;
typedef vector<int> vint;
typedef pair<int, int> pint;
#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for(int i = x; i < n; i++)
template<class T> T RoundOff(T a){ return int(a+.5-(a<0)); }
template<class T, class C> void chmax(T& a, C b){ if(a < b) a = b; }
template<class T, class C> void chmin(T& a, C b){ if(b < a) a = b; }
template<class T, class C> pair<T, C> mp(T a, C b){ return make_pair(a, b); }

char derv(char c1, char c2)
{
	string res("rgb");
	
	res.erase(res.begin() + res.find(c1));
	res.erase(res.begin() + res.find(c2));
	
	return res[0];
}

string conv(string str, int p, char c)
{
	str[p + 0] = c;
	str[p + 1] = c;
	return str;
}

string answer[16][4];

void init()
{
	rep(i, 16)
	{
		answer[i][0] = string().append(i, 'r');
		answer[i][1] = string().append(i, 'g');
		answer[i][2] = string().append(i, 'b');
	}
}

inline bool check(const string& str)
{
	bool res = false;
	
	rep(i, 3) res |= str == answer[str.size()][i];
	
	return 	res;
}

template<class T>
string toString(T sig)
{
	stringstream ss;
	
	ss << sig;
	
	return ss.str();
}

int main()
{
	init();
	
    for(string worm; cin >> worm && worm != "0";)
	{
		int n = worm.size();
		string ans("NA");
		queue<pair<int, string> > que;
		map<string, int> table;
		
		
		for(que.push(mp(0, worm)); !que.empty(); que.pop())
		{
			string sub(que.front().second);
			int times = que.front().first;
			
			if(table[sub] != 0) continue;
			else table[sub] = 1;
			
			if(check(sub))
			{
				ans = toString(times);
				break;
			}
			
			rep(i, sub.size() - 1) if(sub[i] != sub[i + 1])
			{
				char d = derv(sub[i], sub[i + 1]);
				
				que.push(mp(times + 1, conv(sub, i, d)));
			}
		}
		
		cout << ans << endl;
	}
}