#include <iostream>
#include <string>

using namespace std;

int main(void) {
	string N;
	cin >> N;
	if (N.size() > 1 && N[0] == '1') {
		bool invalid = false;
		for (size_t i = 1; i < N.size(); ++i) {
			if (invalid |= (N[i] != '3')) {
				break;
			}
		}
		if (not invalid) {
			cout << N.size() - 1 << endl;
			return 0;
		}
	}
	cout << "-1\n";
	return 0;
}