import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
String s = in.next();
int count = 0;
for(int i=0;i<s.length()-1;i++){
int pre = s.charAt(i)-'0';
int suf = s.charAt(s.length()-1)-'0';
if((pre + suf) % 2 == 0){
count++;
}
}
System.out.println(count);
}
}

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