#include <bits/stdc++.h>
using namespace std;
int main(){
    string S;
    cin >> S;
    vector<int> cnt(26);
    int N = S.size();
    for(int i = 0; i < N; i++){
        cnt[S[i] - 'a']++;
    }
    bool f = false;
    for(int i = 0; i < 26; i++){
        if(cnt[i] == N) f = true;
    }
    if(f){
        if(N % 2 == 1) cout << -1 << endl;
        else cout << 0 << endl;
    }
    else{
        f = true;
        for(int i = 0; i * 2 < N; i++){
            if(S[i] != S[N - 1 - i]) f = false;
        }
        if(f) {
            if(N == 3) cout << -1 << endl;
            else cout << N - 2 << endl;
        }
        else cout << N << endl;
    }

}