import java.util.*;
public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    int c0 = 0;
    int c1 = 0;
    int len = S.length();
    String NS = S;
    int c = 0;
    for(int i = 0;i < len;i++){
      if(S.charAt(i)=='1'){
        c1++;
      }else{
        c0++;
      }
    }
    c = c1;
    if(c1 > c0)c=c0;
    if(c1==0||c0==0)c=0;
    System.out.println(c*2);
  }
} import java.util.*; util.* java public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    int c0 = 0;
    int c1 = 0;
    int len = S.length();
    String NS = S;
    int c = 0;
    for(int i = 0;i < len;i++){
      if(S.charAt(i)=='1'){
        c1++;
      }else{
        c0++;
      }
    }
    c = c1;
    if(c1 > c0)c=c0;
    if(c1==0||c0==0)c=0;
    System.out.println(c*2);
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    int c0 = 0;
    int c1 = 0;
    int len = S.length();
    String NS = S;
    int c = 0;
    for(int i = 0;i < len;i++){
      if(S.charAt(i)=='1'){
        c1++;
      }else{
        c0++;
      }
    }
    c = c1;
    if(c1 > c0)c=c0;
    if(c1==0||c0==0)c=0;
    System.out.println(c*2);
  } main {
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    int c0 = 0;
    int c1 = 0;
    int len = S.length();
    String NS = S;
    int c = 0;
    for(int i = 0;i < len;i++){
      if(S.charAt(i)=='1'){
        c1++;
      }else{
        c0++;
      }
    }
    c = c1;
    if(c1 > c0)c=c0;
    if(c1==0||c0==0)c=0;
    System.out.println(c*2);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String S = sc.next(); S sc.next() sc.next sc int c0 = 0; c0 0 int c1 = 0; c1 0 int len = S.length(); len S.length() S.length S String NS = S; NS S int c = 0; c 0 for(int i = 0;i < len;i++){
      if(S.charAt(i)=='1'){
        c1++;
      }else{
        c0++;
      }
    } int i = 0; int i = 0; i 0 i < len i len i++ i++ i {
      if(S.charAt(i)=='1'){
        c1++;
      }else{
        c0++;
      }
    } {
      if(S.charAt(i)=='1'){
        c1++;
      }else{
        c0++;
      }
    } if(S.charAt(i)=='1'){
        c1++;
      }else{
        c0++;
      } S.charAt(i)=='1' S.charAt(i) S.charAt S i '1' {
        c1++;
      } c1++ c1 {
        c0++;
      } c0++ c0 c = c1 c c1 if(c1 > c0)c=c0; c1 > c0 c1 c0 c=c0 c c0 if(c1==0||c0==0)c=0; c1==0||c0==0 c1==0 c1 0 c0==0 c0 0 c=0 c 0 System.out.println(c*2) System.out.println System.out System System.out c*2 c 2 String[] args args public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    int c0 = 0;
    int c1 = 0;
    int len = S.length();
    String NS = S;
    int c = 0;
    for(int i = 0;i < len;i++){
      if(S.charAt(i)=='1'){
        c1++;
      }else{
        c0++;
      }
    }
    c = c1;
    if(c1 > c0)c=c0;
    if(c1==0||c0==0)c=0;
    System.out.println(c*2);
  }
} public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    int c0 = 0;
    int c1 = 0;
    int len = S.length();
    String NS = S;
    int c = 0;
    for(int i = 0;i < len;i++){
      if(S.charAt(i)=='1'){
        c1++;
      }else{
        c0++;
      }
    }
    c = c1;
    if(c1 > c0)c=c0;
    if(c1==0||c0==0)c=0;
    System.out.println(c*2);
  }
} Main
import java.util.*;
public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    int c0 = 0;
    int c1 = 0;
    int len = S.length();
    String NS = S;
    int c = 0;
    for(int i = 0;i < len;i++){
      if(S.charAt(i)=='1'){
        c1++;
      }else{
        c0++;
      }
    }
    c = c1;
    if(c1 > c0)c=c0;
    if(c1==0||c0==0)c=0;
    System.out.println(c*2);
  }
}
