#include <bits/stdc++.h>

using namespace std;

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

    string t = "1";
    for (auto i = 1; i <= (int) s.length(); ++i) {
        t += '3';
        if (s == t) {
            cout << i << endl;
            return 0;
        }
    }

    cout << -1 << endl;
    return 0;
}