Go: package main

import (
    "bufio"
    "os"
    "fmt"
)

var sc = bufio.NewScanner(os.Stdin)

/**************  Cell  *****************/
type Cell struct {
    item interface{}
    next *Cell
    prev *Cell
}

func NewCell(x interface{}, ne *Cell, pr *Cell) *Cell {
    newCp := new(Cell)
    newCp.item = x
    newCp.next = ne
    newCp.prev = pr
    return newCp
}
/************  End Cell  ***************/

/**************  Queue  ****************/
type Queue struct {
    size int
    front *Cell
    rear *Cell
}

func NewQueue() *Queue {
    return new(Queue)
}

func (q *Queue) Push(x interface{}) {
    newNode := NewCell(x, nil, nil)
    if q.size == 0 {
        q.front = newNode
        q.rear = newNode
    } else {
        newNode.prev = q.rear
        q.rear.next = newNode
        q.rear = newNode
    }
    q.size++
}

func (q *Queue) PopLeft() interface{} {
    if q.size == 0 {
        return nil
    } else {
        x := q.front.item
        if q.size == 1 {
            q.front = nil
            q.rear = nil
        } else {
            q.front = q.front.next
            q.front.prev = nil
        }
        q.size--
        return x
    }
}

func (q *Queue) IsEmpty() bool {
    return q.size == 0
}

func (q *Queue) Length() int {
    return q.size
}

type State struct {
    color string
    cnt int
}

func main() {
    for {
        sc.Scan()
        init := sc.Text()
        if init == "0" {
            break
        }
        bfs(init)
    }
}

func bfs(init string) {
    dic := make(map[string]int)
    que := NewQueue()
    que.Push(State{init, 0})
    length := len(init)
    isSolved := false
    for !que.IsEmpty() {
        state := que.PopLeft().(State)
        _, ok := dic[state.color]
        if ok {
            continue
        } else {
            dic[state.color] = state.cnt
        }

        if isSingleColor(state.color) {
            fmt.Println(state.cnt)
            isSolved = true
            break
        }

        for i := 0;i < length - 1; i++ {
            color1, color2 := string(state.color[i]), string(state.color[i + 1])
            if color1 != color2 {
                color3 := other(color1, color2)
                if i <= length - 2 {
                    que.Push(State{state.color[:i] + color3 + state.color[i + 2:], state.cnt + 1})
                } else {
                    que.Push(State{state.color[:i] + color3, state.cnt + 1})
                }
            }
        }
    }
    if !isSolved {
        fmt.Println("NA")
    }
}

func other(color1, color2 string) string {
    if color1 == "r" {
        if color2 == "g" {
            return "bb"
        } else if color2 == "b" {
            return "gg"
        }
    } else if color1 == "g" {
        if color2 == "r" {
            return "bb"
        } else if color2 == "b" {
            return "rr"
        }
    } else if color1 == "b" {
        if color2 == "r" {
            return "gg"
        } else if color2 == "g" {
            return "rr"
        }
    }
    return ""
}

func isSingleColor(color string) bool {
    for _, c := range color {
        if string(c) != string(color[0]) {
            return false
        }
    }
    return true
}

C++: #include <iostream>
#include <queue>
#include <map>
#define INF 10000000
using namespace std;
typedef pair<string ,int>P;
int cnt;

int bfs(string worm){
  queue<P> que;
  que.push(P(worm,cnt));
  string next;
  char tmp;
  while(!que.empty()){
    P p = que.front();
    que.pop();
    bool f = true;
    for(int i = 0 ; i < p.first.size()-1 ; i++ ){
      if(worm[i] != worm[i+1])f = false;
    }
    if(f)return p.second;
  for(int i = 0 ; i < worm.size()-1 ; i++ ){
    if(worm[i] != worm[i+1]){
      if(worm[i] != 'r' && worm[i+1] != 'r'){
	tmp = 'r';
      }else if(worm[i] != 'g' && worm[i+1] != 'g'){
	tmp = 'g';
      } else {
	tmp = 'b';
      }
      next = worm;
      next[i] = next[i+1] = tmp;
      que.push(P(next,cnt+1));
    }
  }
  }
  return -1;
}

int main(){
  string worm;
  while(cin >> worm){
    if(worm[0] == '0')break;
    cnt = 0;
    int ret = bfs(worm);
    if(ret == -1){
      cout << "NA" << endl;
    }else cout << ret << endl;

  }
  return 0;
}

C++: #include<iostream>
#include<map>
#include<queue>
#include<string>

using namespace std;

int BFS(string);
int ok(string);
char change(char, char);


int main(){

  string s;
  while(1){
    cin >> s;
    if(s == "0") break;
    int res = BFS(s);
    if(res == -1) cout << "NA" << endl;
    else cout << res << endl;
  }
}


int BFS(string s){
  queue<string> Q;
  map<string, int> dist;
  Q.push(s);
  dist[s] = 1;
  while(!Q.empty()){
    string now = Q.front();
    Q.pop();
    if(ok(now) == 1) return dist[now]-1;
    for(int i = 0; i < now.length()-1; i++){
      char res = change(now[i], now[i+1]);
      if(res == '*') continue;

      string tmp = now;
      tmp[i] = tmp[i+1] = res;
      if(dist[tmp] == 0){
	dist[tmp] = dist[now] + 1;
	Q.push(tmp);
      }
    }
  }
  return -1;
}

int ok(string s){
  for(int i = 1; i < s.length(); i++){
    if(s[0] != s[i]) return 0;
  }
  return 1;
}

char change(char c1, char c2){
  string s = "rgb";
  if(c1 == c2) return '*';
    for(int i = 0; i < 3; i++){
      if(c1 != s[i] && c2 != s[i]) return s[i];
    }
}

C++: #include<complex>
#include<algorithm>
#include<iostream>
#include<iomanip>
#include<cmath>
#include<vector>
#include<map>
#include<sstream>
#include<ctime>
#include<cstdio>
#include<cstdlib>
#include<cassert>
#include<deque>
#include<queue>
#include<climits>
#include<list>
#include<stack>
#include<ctime>
#define all(n) n.begin(),n.end()
#define REP(i,s,n) for(int i=s;i<n;i++)
#define rep(i,n) REP(i,0,n)
#define insert(a,b,c,d) PP(P(a,b),P(c,d))
#define F first
#define S second
#define Iter(c) __typeof__((c).begin())
#define foreach(i,c) for(Iter(c) i = (c).begin();i != (c).end();++i)
#define pb push_back
#define INF (1<<27)
#define EPS 1e-10
#define equals(a,b) (fabs((a)-(b)) < EPS)

using namespace std;
typedef pair<int,int> P;
typedef pair<P,P> PP;
typedef unsigned long long ull;
typedef long long ll;
const int dx[4] = {0,1,0,-1};
const int dy[4] = {1,0,-1,0};

typedef pair<string,int> SI;

bool ok(string s)
{
  char c = s[0];
  for(int i=0;i<s.length();i++)
    if(c != s[i])
      return false;
  return true;
}

char getc(char c,char cc)
{
  map<char,bool> index;
  index['r'] = false,index['b'] = false,index['g'] = false;
  index[c] = true;
  index[cc] = true;
  foreach(i,index)
    if(!(*i).S)
      return (*i).F;

}

int solve(string s)
{

  queue<SI> que;
  que.push(SI(s,0));
  map<string,bool> used;
  while(!que.empty())
    {
      SI si = que.front(); que.pop();

      if(used[si.F])
	continue;

      used[si.F] = true;
 
      if(ok(si.F))
	{
	  return si.S;
	}

      if(si.S > 10)
	continue;

      rep(i,si.F.length()-1)
	{
	  if(si.F[i] == si.F[i+1])
	    continue;
	  string news = si.F;
	  news[i] = news[i+1] = getc(si.F[i],si.F[i+1]);
	  que.push(SI(news,si.S+1));
	}

    }

  return -1;
}


int main(){

  while(true)
    {
      string s;
      cin >> s;
      if(s[0] == '0')
	break;

      int ans = solve(s);
      ans != -1?cout << ans << endl:cout << "NA" << endl;

    }

return 0;
}