#include <bits/stdc++.h>
using namespace std;
int main()
{
    string s;
    int c = 0;
    cin >> s;
    for (int i = 1; i < s.length(); i++) {
        if (s[i] != '3') {
            c = -1;
            break;
        } else c++;
    }
    if (s.length() == 1) c = -1;
    cout << c << endl;
    return 0;
}