import java.util.Scanner;
import java.util.Stack;



public class Main {

	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		Stack<Integer> stack = new Stack<Integer>();
		stack.push(s.charAt(0)-'0');
		int count =0;
		for(int i=1;i<s.length();i++) {
			if (stack.isEmpty()) {
				stack.push(s.charAt(i)-'0');
			} else {
				if (stack.peek()!=(s.charAt(i)-'0')) {
					stack.pop();
					count+=2;
				} else {
					stack.push(s.charAt(i)-'0');
				}
			}
		}
		System.out.println(count);
	}
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz