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 <stack>
#include <vector>
#include <stdio.h>
#include <algorithm>
#include <string>
#include <cstring>
#include <cmath>
#include <complex>
#include <map>
#include <set>
#include <climits>
using namespace std;

#define rep(i,n) for(int i=0;i<int(n);++i)
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define EPS 1e-8
#define F first
#define S second

static const double PI=6*asin(0.5);
typedef long long ll;
typedef complex<double> CP;
typedef pair<int,int> P;
static const int INF=1<<24;

string s;
string qf;
/*
int foo1(int D[]){
	int res=0;
	for(int i=0;i<s.size();i++){
		res*=10;
		res+=D[i];
	}
	return res;
}
void foo2(int D[],int m){
	rep(j,s.size()){
		D[j]=0;
	}
	for(int i=s.size()-1;i>=0;--i){
		D[i]=m%10;
		m/=10;
		rep(j,s.size()){
		}
	}
}
*/
set<string> vis;

bool check(string a){
	char t=a[0];
	rep(i,s.size()){
		if(t!=a[i]) return false;
	}
	return true;
}

int main(){
	
	while(cin>>s,s[0]!='0'){
		vis.clear();
		int ans=-1;
		queue<string> qu;
		if(check(s)){
			cout<<"0"<<endl;
			continue;
		}
		vis.insert(s);
		qu.push(s);
		bool f=false;
		bool f1=false;
		//int c=0;
		while(!qu.empty()&&!f1){
			//c++;
			//if(c>50) break;
			f=false;
			ans++;
			int qs=qu.size();
			rep(i,qs){
				qf=qu.front();
				//cout<<qf<<endl;
				qu.pop();
				if(check(qf)){
					cout<<ans<<endl;
					f1=true;
					break;
				}
				rep(j,s.size()-1){
					if(qf[j]!=qf[j+1]){
						string tmp=qf;
						tmp[j] = tmp[j+1] = 'r'+'g'+'b'-qf[j]-qf[j+1];
						if(vis.find(tmp)==vis.end()){
							qu.push(tmp);
							vis.insert(tmp);
							f=true;
						}
					}
				}
				if(!f) break;
			}
			if(f1) break;
		}
		if(f1) continue;
		if(!f&&!f1) cout<<"NA"<<endl;
		
	}
	
	return 0;
}

/*
int main(){
	
	while(cin>>s,s[0]!='0'){
		vis.clear();
		int ans=0;
		queue<int> qu;
		rep(i,s.size()){
			if(s[i]=='r') a[i]=0;
			else if(s[i]=='g') a[i]=1;
			else if(s[i]=='b') a[i]=2;
		}
		if(check()){
			cout<<"0"<<endl;
			continue;
		}
		
		qu.push(foo1(a));
		vis.insert(foo1(a));
		bool f=false;
		bool f1=false;
		//int c=0;
		while(!qu.empty()&&!f1){
			//c++;
			//if(c>50) break;
			f=false;
			ans++;
			int qs=qu.size();
			rep(i,qs){
				qf=qu.front();
				qu.pop();
				foo2(a,qf);
				if(check()){
					cout<<ans-1<<endl;
					f1=true;
					break;
				}
				rep(j,s.size()-1){
					if(a[j]!=a[j+1]){
						rep(k,s.size()){
							tmp[k]=a[k];
						}
						if(a[j]*a[j+1]==2){
							tmp[j]=0;
							tmp[j+1]=0;
						}
						else if(a[j]==2||a[j+1]==2){
							tmp[j]=1;
							tmp[j+1]=1;
						}
						else{
							tmp[j]=2;
							tmp[j+1]=2;
						}
						if(vis.find(foo1(tmp))==vis.end()){
							qu.push(foo1(tmp));
							vis.insert(foo1(tmp));
							f=true;
						}
					}
				}
				if(!f) break;
			}
			if(f1) break;
		}
		if(f1) continue;
		if(!f&&!f1) cout<<"NA"<<endl;
		
	}
	
	return 0;
}
*/

C++: #include <iostream>
#include <string>
#include <queue>
#include <map>
using namespace std;

int main(){
  int i,j,k,n;
  string str,ans,a1,a2,a3;
  while(1){
    cin >> str;
    if(str == "0") break;
    queue <string> Q;
    map <string,int> d,f;

    a1 = "r";
    a2 = "b";
    a3 = "g";
    for(i=1;i<str.size();i++){
    a1 += "r";
    a2 += "b";
    a3 += "g";
  }

    d[str] = 0;
    Q.push(str);
    ans = "NA";

    while(!Q.empty()){
      string u,v;
      u = Q.front();
      Q.pop();
      f[u] = 1;
      if(u == a1 || u == a2 || u == a3){
	ans = u;
	break;
      }

      for(i=0;i<u.size()-1;i++){
	if(u[i] == 'r' && u[i+1] == 'g' || u[i] == 'g' && u[i+1] == 'r'){
	  v = u;
	  v[i] = v[i+1] = 'b';
	  
	  if(!f[v]){
	    d[v] = d[u] + 1;
	    Q.push(v);
	    f[v] = 1;
	  }
	}

	else if(u[i] == 'r' && u[i+1] == 'b' || u[i] == 'b' && u[i+1] == 'r'){
	  v = u;
	  v[i] = v[i+1] = 'g';

	  if(!f[v]){
	    d[v] = d[u] + 1;
	    Q.push(v);
	    f[v] = 1;
	  }
	}
	
	else if(u[i] == 'g' && u[i+1] == 'b' || u[i] == 'b' && u[i+1] == 'g'){
	  v = u;
	  v[i] = v[i+1] = 'r';
	  
	  if(!f[v]){
	    d[v] = d[u] + 1;
	    Q.push(v);
	    f[v] = 1;
	  }
	}
      }
    }
    if(ans != "NA") cout << d[ans] << endl;
    else cout << "NA" << endl;
  }
  return 0;
}