#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#include <list>
#include <atcoder/all>
#define popcount __builtin_popcount
using namespace std;
using namespace atcoder;
typedef long long ll;
typedef pair<int, int> P;

int main()
{
    string s; cin>>s;
    int n=s.size();
    if(n==3){
        if(s[0]==s[2] && s[0]!=s[1]){
            cout<<-1<<endl;
            return 0;
        }
    }
    bool same=1, p=1;
    for(int i=0; i<n; i++){
        if(s[i]!=s[0]) same=0;
        if(s[i]!=s[n-1-i]) p=0;
    }
    if(same) cout<<-n%2<<endl;
    else if(p) cout<<n-2<<endl;
    else cout<<n<<endl;
    return 0;
}