import java.util.Scanner;

class Main{
  public static void main(String... args){
    char[] s = new Scanner(System.in).next().toCharArray();
    int[] arr = {0,0};
    
    for(char c : s){
      if(c == '1')arr[1]++;
      else arr[0]++;
    }
    
    
    System.out.println(2*Math.min(arr[0],arr[1]));
  }
} import java.util.Scanner; Scanner java.util class Main{
  public static void main(String... args){
    char[] s = new Scanner(System.in).next().toCharArray();
    int[] arr = {0,0};
    
    for(char c : s){
      if(c == '1')arr[1]++;
      else arr[0]++;
    }
    
    
    System.out.println(2*Math.min(arr[0],arr[1]));
  }
} Main public static void main(String... args){
    char[] s = new Scanner(System.in).next().toCharArray();
    int[] arr = {0,0};
    
    for(char c : s){
      if(c == '1')arr[1]++;
      else arr[0]++;
    }
    
    
    System.out.println(2*Math.min(arr[0],arr[1]));
  } main {
    char[] s = new Scanner(System.in).next().toCharArray();
    int[] arr = {0,0};
    
    for(char c : s){
      if(c == '1')arr[1]++;
      else arr[0]++;
    }
    
    
    System.out.println(2*Math.min(arr[0],arr[1]));
  } char[] s = new Scanner(System.in).next().toCharArray(); s new Scanner(System.in).next().toCharArray() new Scanner(System.in).next().toCharArray new Scanner(System.in).next() new Scanner(System.in).next new Scanner(System.in) int[] arr = {0,0}; arr {0,0} 0 0 for(char c : s){
      if(c == '1')arr[1]++;
      else arr[0]++;
    } char c s {
      if(c == '1')arr[1]++;
      else arr[0]++;
    } {
      if(c == '1')arr[1]++;
      else arr[0]++;
    } if(c == '1')arr[1]++;
      else arr[0]++; c == '1' c '1' arr[1]++ arr[1] arr 1 arr[0]++ arr[0] arr 0 System.out.println(2*Math.min(arr[0],arr[1])) System.out.println System.out System System.out 2*Math.min(arr[0],arr[1]) 2 Math.min(arr[0],arr[1]) Math.min Math arr[0] arr 0 arr[1] arr 1 String... args args
import java.util.Scanner;

class Main{
  public static void main(String... args){
    char[] s = new Scanner(System.in).next().toCharArray();
    int[] arr = {0,0};
    
    for(char c : s){
      if(c == '1')arr[1]++;
      else arr[0]++;
    }
    
    
    System.out.println(2*Math.min(arr[0],arr[1]));
  }
}
