#include <iostream>
#include <string>
using namespace std;
int main()
{
	string N;
	int c=0;
	cin >> N;
	for (int i = 1; i < N.size(); i++)
	{
		if (N[i] != '3')
		{
			c = -1;
			break;
		}

		c++;
	}

	cout << c << endl;
	return 0;
}