#include <algorithm>
#include <cmath>
#include <climits>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <cassert>
#include <functional>

using namespace std;

#define LOG(...) printf(__VA_ARGS__)
//#define LOG(...)
#define FOR(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define RSORT(c) sort((c).rbegin(),(c).rend())
#define CLR(a) memset((a), 0 ,sizeof(a))

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int dx[] = { -1, 0, 1, 0 }; const int dy[] = { 0, 1, 0, -1 };
struct nc{
	int number;
	int count;
};
int main() {
	map<string, int> msi;
	FOR(i, 2, 11){
		queue<string> qs;
		REP(j, 3){
			string s2;
			if (j == 0)REP(k, i)s2 += 'r';
			if (j == 1)REP(k, i)s2 += 'g';
			if (j == 2)REP(k, i)s2 += 'b';
			msi.insert({ s2, 0 });
			qs.push(s2);
		}
		while (!qs.empty()){
			string s3 = qs.front(); qs.pop();
			REP(j, i - 1){
				if (s3[j] == 'r' && s3[j + 1] == 'r'){
					string s4 = s3;
					s4[j] = 'g'; s4[j+1] = 'b';
					if (msi.find(s4) == msi.end()){
						msi.insert({ s4, msi[s3] + 1 });
						qs.push(s4);
					}
					s4[j] = 'b'; s4[j + 1] = 'g';
					if (msi.find(s4) == msi.end()){
						msi.insert({ s4, msi[s3] + 1 });
						qs.push(s4);
					}
				}
				if (s3[j] == 'g' && s3[j + 1] == 'g'){
					string s4 = s3;
					s4[j] = 'b'; s4[j + 1] = 'r';
					if (msi.find(s4) == msi.end()){
						msi.insert({ s4, msi[s3] + 1 });
						qs.push(s4);
					}
					s4[j] = 'r'; s4[j + 1] = 'b';
					if (msi.find(s4) == msi.end()){
						msi.insert({ s4, msi[s3] + 1 });
						qs.push(s4);
					}
				}
				if (s3[j] == 'b' && s3[j + 1] == 'b'){
					string s4 = s3;
					s4[j] = 'r'; s4[j + 1] = 'g';
					if (msi.find(s4) == msi.end()){
						msi.insert({ s4, msi[s3] + 1 });
						qs.push(s4);
					}
					s4[j] = 'g'; s4[j + 1] = 'r';
					if (msi.find(s4) == msi.end()){
						msi.insert({ s4, msi[s3] + 1 });
						qs.push(s4);
					}
				}
			}
		}
	}

	string s;
	while (cin >> s, s != "0"){
		if (msi.find(s) != msi.end()){
			cout << msi[s] << endl;
		}
		else{
			cout << "NA" << endl;
		}
	}
}