import java.util.*;
import java.util.stream.*;

public class Main {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    char[] S = in.nextLine().toCharArray();
    int zero = 0, one = 0;
    for (char ch : S) {
      if (ch == '0') {
        zero++;
      } else {
        one++;
      }
    }
    System.out.println(Math.min(zero, one) * 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