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 <cstdio>
#include <algorithm>
#include <vector>
#include <sstream>
#include <cmath>
#include <queue>

#define INF (1 << 21)

using namespace std;

int N;

int check[1000000];

queue<string> que, que_next;

int index(string str){
	
	int ref = 0;
	
	for(int i = 0; i < N; i++){
		ref += str[i] - '0';
		ref *= 3;
	}
	
	return ref;
}

int main(){
	
	while(true){
		string str;
		cin >> str;
		
		queue<string> que_emp;
		
		que = que_emp;
		que_next = que_emp;
		
		for(int i = 0; i < 1000000; i++){
			check[i] = INF;
		}
		
		if(str[0] == '0'){
			break;
		}else{
			N = str.size();
			for(int i = 0; i < N; i++){
				if(str[i] == 'r'){
					str[i] = '0';
				}else if(str[i] == 'b'){
					str[i] = '1';
				}else{
					str[i] = '2';
				}
			}
		}
		
		que.push(str);
		
		int depth = 0;
		
		while(true){
			while(!que.empty()){
				string str = que.front();
				que.pop();
				if(check[index(str)] != INF){
					continue;
				}
				check[index(str)] = depth;
				for(int i = 0; i < N - 1; i++){
					if(str[i] != str[i + 1]){
						string str_copy = str;
						if(str[i] != '0' && str[i + 1] != '0'){
							str_copy[i] = '0';
							str_copy[i + 1] = '0';
						}else if(str[i] != '1' && str[i + 1] != '1'){
							str_copy[i] = '1';
							str_copy[i + 1] = '1';
						}else{
							str_copy[i] = '2';
							str_copy[i + 1] = '2';
						}
						que_next.push(str_copy);
					}
				}
			}
			que = que_next;
			que_next = que_emp;
			depth++;
			if(que.empty()){
				break;
			}
			//cout << depth << " " << que.size() << endl;;
		}
		
		string check_0 = "";
		string check_1 = "";
		string check_2 = "";
		
		for(int i = 0; i < N; i++){
			check_0 = check_0 + "0";
			check_1 = check_1 + "1";
			check_2 = check_2 + "2";
		}
		
		int ans = min(min(check[index(check_0)], check[index(check_1)]), check[index(check_2)]);
		
		if(ans == INF){
			cout << "NA" << endl;
		}else{
			cout << ans << endl;
		}
		
	}
	
	return 0;
}