#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=1000000007,MAX=105,INF=1<<30;

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    string S;cin>>S;
    string T=S;
    sort(all(T));
    if(T[0]==T.back()){
        if(si(S)&1) cout<<-1<<endl;
        else cout<<0<<endl;
    }else{
        T=S;
        reverse(all(T));
        if(S!=T){
            cout<<si(S)<<endl;
        }else{
            if(si(S)==3) cout<<-1<<endl;
            else cout<<si(S)-2<<endl;
        }
    }
}