——）——————

#include <iostream>
#include <iomanip>
using namespace std;

int main() {
	int n, c = 0;
	cin >> n;

	while (n != 0) {
		int x = n % 10;

		if (x == 0 || x == 2 || x == 4 || x == 6 || x == 8) {
			c++;
		}

		n /= 10;
	}

	cout << c;
}