import std.stdio, std.array, std.string, std.conv, std.algorithm;
import std.typecons, std.range, std.random, std.math, std.container;
import std.numeric, std.bigint, core.bitop;

void main() {
    auto S = readln.chomp;
    if (S.length % 2 == 1) {
        if (is_onaji(S)) {
            writeln(-1);
        } else if (is_kaibun(S)) {
            auto mid = S.length.to!int/2;
            if (S[mid] != S.front && is_onaji(S[0..mid] ~ S[mid+1..$])) {
                writeln(-1);
            } else {
                writeln(S.length.to!int - 2);
            }
        } else {
            writeln(S.length);
        }
    } else {
        if (is_onaji(S) ) {
            writeln(0);
        } else if (is_kaibun(S)) {
            writeln(S.length.to!int - 2);
        } else {
            writeln(S.length);
        }
    }

}

bool is_kaibun(string S) {
    foreach (i; 0..S.length.to!int/2) {
        if (S[i]  != S[S.length.to!int-i-1]) return false;
    }
    return true;
}

bool is_onaji(string S) {
    foreach (i; 1..S.length) if (S[i] != S.front) return false;
    return true;
}