import java.awt.geom.Point2D;
import java.io.*;
import java.math.BigInteger;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Deque;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.PriorityQueue;
import java.util.Scanner;
import java.util.Stack;
import java.util.TreeMap;



public class Main {

	static PrintWriter out = new PrintWriter(System.out);
	static FastScanner sc = new FastScanner();
	static Scanner stdIn = new Scanner(System.in);

	public static void main(String[] args) {
		solv();
		while(true) {
			String in = sc.next();
			if(in.equals("0")) break;
			if(!map.containsKey(in)) {
				out.println("NA");
			}
			else {
				out.println(map.get(in));
			}
		}
		out.flush();
	}
	static ArrayDeque<Data> queue = new ArrayDeque<Data>();
	static HashMap<String, Integer> map = new HashMap<String, Integer>();
	static char[] X = new char[] {'r','g','b'};
	static void solv() {
		for(int i = 2; i <= 10; i++) {
			for(int j = 0; j < 3; j++) {
				char[] str = new char[i];
				Arrays.fill(str, X[j]);
				queue.add(new Data(str,0));
				
				while(!queue.isEmpty()) {
					bfs(queue.poll());
				}
			}
		}
	}
	
	static void bfs(Data a) {
		String tmp = String.valueOf(a.data);
		if(map.containsKey(tmp) && map.get(tmp) <= a.count) return;
		map.put(tmp, a.count);
		char[] k = a.data;
		for(int i = 0; i < k.length-1; i++) {
			if(k[i] == k[i+1]) {
				if(k[i] == 'r') {
					char[] cpy = Arrays.copyOf(k, k.length);
					cpy[i] = 'g';
					cpy[i+1] = 'b';
					queue.addLast(new Data(cpy,a.count+1));
					cpy = Arrays.copyOf(k, k.length);
					cpy[i] = 'b';
					cpy[i+1] = 'g';
					queue.addLast(new Data(cpy,a.count+1));
				}
				if(k[i] == 'g') {
					char[] cpy = Arrays.copyOf(k, k.length);
					cpy[i] = 'r';
					cpy[i+1] = 'b';
					queue.addLast(new Data(cpy,a.count+1));
					cpy = Arrays.copyOf(k, k.length);
					cpy[i] = 'b';
					cpy[i+1] = 'r';
					queue.addLast(new Data(cpy,a.count+1));
				}
				if(k[i] == 'b') {
					char[] cpy = Arrays.copyOf(k, k.length);
					cpy[i] = 'g';
					cpy[i+1] = 'r';
					queue.addLast(new Data(cpy,a.count+1));
					cpy = Arrays.copyOf(k, k.length);
					cpy[i] = 'r';
					cpy[i+1] = 'g';
					queue.addLast(new Data(cpy,a.count+1));
				}
			}
		}
	}

	
	

}

class Data {
	char[] data;
	int    count;
	Data(char[] a, int b) {
		data = a;
		count = b;
	}
	
}
//------------------------------//
//-----------//
class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }
    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
    private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
    private void skipUnprintable() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;}
    public boolean hasNext() { skipUnprintable(); return hasNextByte();}
    public String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while(isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }
    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
    
    public int nextInt() {
    	 if (!hasNext()) throw new NoSuchElementException();
         int n = 0;
         boolean minus = false;
         int b = readByte();
         if (b == '-') {
             minus = true;
             b = readByte();
         }
         if (b < '0' || '9' < b) {
             throw new NumberFormatException();
         }
         while(true){
             if ('0' <= b && b <= '9') {
                 n *= 10;
                 n += b - '0';
             }else if(b == -1 || !isPrintableChar(b)){
                 return minus ? -n : n;
             }else{
                 throw new NumberFormatException();
             }
             b = readByte();
         }
    }
    
    public double nextDouble() {
    	return Double.parseDouble(next());
    }
    

}

Measured memory_bytes: 61448