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