import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String str  = sc.next();
    sc.close();
    int one = 0, zero = 0;
    for (int i = 0; i < str.length(); i++) {
      if (str.charAt(i) == '0') {
        zero++;
      } else {
        one++;
      }
    }
    System.out.println(2 * Math.min(one, zero));
  }
}
/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