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<string>
#include<map>
#include<queue>
using namespace std;

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

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

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];
  }
}

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

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))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;
}

C++: #include<iostream>
#include<string>
#include<queue>
#include<set>
#define psi pair<string, int>

using namespace std;

bool check(string str){
    return (str[0]!=str[1]);
}

bool same(string str){
    for(int i=0; i<str.size(); i++){
        if(str[0]!=str[i]) return false;
    }
    return true;
}

char getColor(string str){
    char c1=min(str[0], str[1]);
    char c2=max(str[0], str[1]);
    if(c1=='b'&&c2=='g') return 'r';
    if(c1=='b'&&c2=='r') return 'g';
    if(c1=='g'&&c2=='r') return 'b';
}
int solve(string str){
    queue<psi> qu;
    qu.push(psi(str, 0));
    set<string> done;

    while(!qu.empty()){
        psi w=qu.front(); qu.pop();
        string s=w.first;
        done.insert(s);

        if(same(s)){
            return w.second;
        }

        for(int i=0; i<s.size()-1; i++){
            if(check(s.substr(i, 2))){
                char new_color=getColor(s.substr(i, 2));
                string nx=s;
                nx[i+1]=nx[i]=new_color;
                if(done.count(nx)==1) continue;
                //cout<< nx<< endl;
                qu.push(psi(nx, w.second+1));
                done.insert(nx);
            }
        }
    }
    return -1;
}
int main(){

    while(1){
        string s;
        cin>> s;
        if(s=="0") break;

        int ans=solve(s);
        if(ans==-1){
            cout<< "NA"<< endl;
        }else{
            cout<< ans<< endl;
        }
    }

    return 0;
}

C++: #include <iostream>
#include <set>
#include <queue>

struct Worm {
	std::string body;
	int step;
	Worm() {}
	Worm(std::string body, int step) : body(body), step(step) {}
};

bool meetColor(std::string body)
{
	char c = body[0];
	for (int i=1; i<body.length(); i++) {
		if (body[i] != c) return false;
	}
	return true;
}

int getMinStep(std::queue<Worm> que, std::set<std::string>& checked)
{
	while (!que.empty()) {
		Worm worm = que.front(); que.pop();
		if (meetColor(worm.body)) return worm.step;
		if (checked.find(worm.body) != checked.end()) continue;
		checked.insert(worm.body);
		for (int i=0; i<worm.body.length()-1; i++) {
			if (worm.body[i] == worm.body[i+1]) continue;
			std::string new_body = worm.body;
			if (new_body[i] == 'r' && new_body[i+1] == 'g') new_body[i] = new_body[i+1] = 'b';
			else if (new_body[i] == 'r' && new_body[i+1] == 'b') new_body[i] = new_body[i+1] = 'g';
			else if (new_body[i] == 'g' && new_body[i+1] == 'r') new_body[i] = new_body[i+1] = 'b';
			else if (new_body[i] == 'g' && new_body[i+1] == 'b') new_body[i] = new_body[i+1] = 'r';
			else if (new_body[i] == 'b' && new_body[i+1] == 'r') new_body[i] = new_body[i+1] = 'g';
			else new_body[i] = new_body[i+1] = 'r';
			que.push(Worm(new_body, worm.step+1));
		}
	}
	return -1;
}

int main()
{
	std::string worm;
	while (true) {
		std::cin >> worm;
		if (worm=="0") break;
		std::queue<Worm> que;
		que.push(Worm(worm,0));
		std::set<std::string> checked;
		int res = getMinStep(que, checked);
		if (res >= 0) std::cout << res << std::endl;
		else std::cout << "NA" << std::endl;
	}
	return 0;
}