#include<bits/stdc++.h>
using namespace std;
using ll = long long int;
using ld = long double;
const ll MAX = 5000000000000000000;
const ld PI = 3.14159265358979;
const ll MOD = 0;//2024948111;
ld dotorad(ld K){return PI * K / 180.0;}
ld radtodo(ld K){return K * 180.0 / PI;}
mt19937 mt;
void randinit(){srand((unsigned)time(NULL));mt = mt19937(rand());}
int main(){
    string S;
    cin >> S;
    ll N = S.size();
    for(ll i = 0;i < N;i++){
        if(S[i] != S[N - 1 - i]){
            cout << N << endl;
            return 0;
        }
    }
    if(N % 2 == 0){
        vector<ll> A(500,0);
        ll a = 0;
        for(ll i = 0;i < N / 2;i++){
            if(A[S[i] - 'a'] == 0){
                a++;
                A[S[i] - 'a'] = 1;
            }
        }
        if(a >= 2){
            cout << N - 2 << endl;
            return 0;
        }
        cout << 0 << endl;
    }
    else{
        ll m = N / 2;
        vector<ll> A(500,0);
        ll a = 0;
        for(ll i = 0;i < m;i++){
            if(A[S[i] - 'a'] == 0){
                a++;
                A[S[i] - 'a'] = 1;
            }
        }
        if(a >= 2){
            cout << N - 2 << endl;
            return 0;
        }
        if(N <= 3){
            cout << -1 << endl;
            return 0;
        }
        if(S[0] == S[m]){
            cout << -1 << endl;
            return 0;
        }
        cout << N - 2 << endl;
        return 0;
    }
}