#include <bits/stdc++.h>
using namespace std;

struct iofast_t {
    iofast_t() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} iofast;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return std::vector(arg, init);
    else return std::vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

template <typename T, typename Compare = less<T>>
T &chmin(T &l, T r, Compare &&f = less<T>()) { return l = min(l, r, f); }
template <typename T, typename Compare = less<T>>
T &chmax(T &l, T r, Compare &&f = less<T>()) { return l = max(l, r, f); }

int main() {
    string s; cin >> s;

    if (count(begin(s), end(s), s[0]) == size(s)) {
        cout << -int(size(s) % 2) << endl;
        return 0;
    }

    if (!equal(begin(s), end(s), rbegin(s))) {
        cout << size(s) << endl;
        return 0;
    }

    if (size(s) <= 3) {
        cout << -1 << endl;
        return 0;
    }

    cout << size(s) - 2 << endl;
}