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 <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <cstring>
#include <climits>
#include <sstream>
#include <cstdio>
using namespace std;
static const double EPS = 1e-5;
typedef long long ll;


int ans;
set<string> memo;
queue<string> q;
bool na;

void bfs(){
	//cout<<ans<<endl;
	queue<string> nq;
	
	while(!q.empty()){
		string ss=q.front();q.pop();
		if(memo.count(ss)){
			//cout<<ss<<" finded"<<endl;
			continue;
		}
		//cout<<ss<<endl;
		memo.insert(ss);
		bool end=true;
		for(int i=0;i<ss.size()-1;i++)if(ss[i]!=ss[i+1])end=false;
		if(end){
			//cout<<ss<<" "<<ans<<endl;
			return ;
		}

		for(int i=0;i<ss.size()-1;i++){
			if(ss[i]!=ss[i+1]){
				string sss(ss);
				if(ss[i]!= 'r' && ss[i+1]!='r')sss[i]=sss[i+1]='r';
				if(ss[i]!= 'g' && ss[i+1]!='g')sss[i]=sss[i+1]='g';
				if(ss[i]!= 'b' && ss[i+1]!='b')sss[i]=sss[i+1]='b';
				nq.push(sss);
			}
		}
	}
	if(!nq.empty()){
		++ans;
		q=nq;
		bfs();
	}else na=true;
}


main(){
	string ss;
	while(cin>>ss){
		if(ss[0]=='0')break;
		ans=0;
		na=false;
		memo.clear();
		while(!q.empty())q.pop();
		q.push(ss);
		bfs();
		if(na)cout<<"NA"<<endl;
		else cout<<ans<<endl;
	}
}

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

using namespace std;

inline bool ok(const string & v){
    for (int i = 1; i < v.size(); i++){
        if (v[i] != v[0]) return false;
    }
    return true;
};

inline char other(char a, char b){
    if (a>b)swap(a, b);
    if (a == 'g' && b == 'r'){
        return 'b';
    }
    if (a == 'b' && b == 'g'){
        return 'r';
    }
    if (a == 'b' && b == 'r'){
        return 'g';
    }
    throw "";
}

struct state {
    string str;
    int n;
};

int main(){
    string s;
    while (cin >> s, s != "0"){
        queue<state> q;
        set<string> dp;
        q.push({ s, 0 });

        int ans = -1;
        while (q.size()){
            state sta = q.front();
            q.pop();
            string & sv = sta.str;
            auto pr = dp.insert(sv);
            if (!pr.second){
                continue;
            }
            if (ok(sv)){
                ans = sta.n;
                break;
            }
            for (int i = 1; i < sv.size(); i++){
                if (sv[i] != sv[i - 1]){
                    char a = sv[i];
                    char b = sv[i - 1];
                    sv[i] = sv[i - 1] = other(a, b);
                    q.push({ sv, sta.n + 1 });
                    sv[i] = a;
                    sv[i - 1] = b;
                }
            }
        }
        if (ans == -1){
            cout << "NA" << endl;
        }
        else{
            cout << ans << endl;
        }
    }
}

C++: #include <iostream>
#include <queue>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <map>
#include <string>
using namespace std;

const int INF = 1e+9;
typedef pair<string, int> P;

int ans = 0;
int s_size;

string change(string s, int a, int b){
	if((s[a] == 'r' && s[b] == 'g') || (s[a] == 'g' && s[b] == 'r'))
		s[b] = s[a] = 'b';
	else if((s[a] == 'b' && s[b] == 'g') || (s[a] == 'g' && s[b] == 'b'))
		s[b] = s[a] = 'r';
	else
		s[b] = s[a] = 'g';
	
	return s;
}

int main() {
	std::ios::sync_with_stdio(false);
    std::cin.tie(0);
	string str;
	while(cin >> str){
		if(str == "0")
			break;
		s_size = str.size();
		ans = INF;
		queue<P> que;
		map<string, bool> visited;
		que.push(P(str, 0));
		while(!que.empty()){
			P p = que.front();
			que.pop();
			string s = p.first;
			if(visited[s])
				continue;
			visited[s] = true;
			bool flag = false;
			for(int i = 0; i < s_size - 1; ++i){
				if(s[i] != s[i + 1])
					break;
				if(i == s_size - 2){
					ans = min(ans, p.second);
					flag = true;
					break;
				}
			}
			if(flag)
				continue;
			for(int i = 0; i < s_size - 1; ++i){
				if(s[i] != s[i + 1]){
					string t = change(s, i, i + 1);
					que.push(P(t, p.second + 1));
				}
			}
		}
		end:
		if(ans == INF)
			cout << "NA" << endl;
		else
			cout << ans << endl;
	}
	return 0;
}