#include <iostream>
using namespace std;
int main() {
long x;
int c = 0;
cin >> x;
while (x/10) {
int t = x%10;
int u = x&100 / 10;
if ((t+u)%2 == 0){
c++;
}
x /= 10;
}
cout << c;
return 0;
}
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