import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int cnt = 0;
        int red = 0;
        int blue = 0;
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == '0') {
                red++;
            } else {
                blue++;
            }
            if (i != s.length() - 1 && s.charAt(i) != s.charAt(i + 1)) {
                cnt++;
            }
        }
        int temp = Math.min(red - cnt, blue - cnt);
        System.out.println(cnt * 2 + temp * 2);
    }
}
/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