#include<bits/stdc++.h>
using namespace std;

#define int long long
typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define all(v) (v).begin(),(v).end()
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
#define pb push_back
#define mp make_pair
#define fi first
#define se second
template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}

signed main(){
    string S;
    while(cin>>S,S!="0"){
        map<string,int>dist;
        dist[S]=0;

        queue<string>que;
        que.push(S);
        while(que.size()){
            string s=que.front();
            que.pop();

            for(int i=0;i+1<s.size();i++){
                if(s[i]==s[i+1])continue;
                int c;
                rep(j,3)if("rgb"[j]!=s[i]&&"rgb"[j]!=s[i+1])c=j;
                string ss=s;
                ss[i]=ss[i+1]="rgb"[c];
                if(dist.find(ss)!=dist.end())continue;
                dist[ss]=dist[s]+1;
                que.push(ss);
            }
        }

        int mi=1001001001;
        rep(i,3){
            string s=string(S.size(),"rgb"[i]);
            if(dist.find(s)!=dist.end())chmin(mi,dist[s]);
        }

        if(mi==1001001001)cout<<"NA"<<endl;
        else cout<<mi<<endl;
    }
    return 0;
}