import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
while (scanner.hasNextLine()) {
String inputStr = scanner.nextLine().trim();
int charONums = countOccurrences(inputStr, 'o');
if (charONums % 2 == 0) {
System.out.println(inputStr.length());
} else {
System.out.println(inputStr.length() - 1);
}
}
scanner.close();
}
private static int countOccurrences(String str, char ch) {
int count = 0;
for (int i = 0; i < str.length(); i++) {
if (str.charAt(i) == ch) {
count++;
}
}
return count;
}
}