#include<iostream>
#include<algorithm>
#include <vector>
using namespace std;
int main() {
	string A;
	int cnta = 0;
	int cntb = 0;
	cin >> A;
	int Z;
	Z = A.size();
	for (int i = 1; i < Z - 1; i++) {
		if (A.at(i) != A.at(i + 1)) {
			cnta++;
		}
	}
	if (A.at(0) != A.at(1)) {
		cntb++;
	}
	if (cnta == 0 && cntb == 1) {
		cout << Z - 1 << endl;
	}
	if (cnta != 0 || cntb != 1) {
		cout << -1 << endl;
	}
}