import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] s = sc.next().toCharArray();
		Deque<Integer> deq = new ArrayDeque<Integer>();

		int count = 1;
		for (int i = 1; i < s.length; i++) {
			if(s[i]==s[i-1]) {
				count++;
			}else {
				deq.addLast(count);
				count = 1;
			}
		}
		deq.addLast(count);

		int ans = deq.pollFirst();
		while(!deq.isEmpty()) {
			ans = deq.pollFirst()-ans;
		}
		System.out.println(s.length-Math.abs(ans));
		sc.close();
	}
}
/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