#include<bits/stdc++.h>
using namespace std;
#define int long long
#define REP(i,m,n) for(int i=(m);i<(n);i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define all(a) a.begin(),a.end()
#define rall(c) (c).rbegin(),(c).rend()
#define mp make_pair
#define endl '\n'
//#define vec vector<ll>
//#define mat vector<vector<ll> >
#define fi first
#define se second
#define double long double
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
//typedef long double ld;
typedef complex<double> Complex;
const ll INF=1e9+7;
const ll MOD=998244353;
const ll inf=INF*INF;
const ll mod=INF;
const ll MAX=1000010;
const double PI=acos(-1.0);
typedef vector<vector<ll> > mat;
typedef vector<ll> vec;





signed main(){
    string s;cin>>s;
    ll n=s.size();
    string t=s;
    reverse(all(t));
    bool f=0;
    if(t!=s){
        cout<<n<<endl;
        return 0;
    }
    vector<ll>cnt(26);
    rep(i,n/2){
        cnt[s[i]-'a']++;
    }
    ll c=0;
    rep(i,26){
        if(cnt[i])c++;
    }
    if(c>1)f=1;
    sort(all(s));
    if(s[0]==s[n-1]&&n%2==0){
        cout<<0<<endl;
        return 0;
    }
    if(n%2&&n>=5&&f==0&&s[0]!=s[n-1]){
        f=1;
    }
    cout<<(f?n-2:-1)<<endl;
}