import java.util.*;

public class Main{

    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        
        String S = sc.next();
        sc.close();

        int count0 = 0;
        int count1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) == '1')
                count1++;
            if(S.charAt(i) == '0')
                count0++;
        }
        System.out.println(2*Math.min(count1,count0));
    }
} import java.util.*; util.* java public class Main{

    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        
        String S = sc.next();
        sc.close();

        int count0 = 0;
        int count1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) == '1')
                count1++;
            if(S.charAt(i) == '0')
                count0++;
        }
        System.out.println(2*Math.min(count1,count0));
    }
} Main public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        
        String S = sc.next();
        sc.close();

        int count0 = 0;
        int count1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) == '1')
                count1++;
            if(S.charAt(i) == '0')
                count0++;
        }
        System.out.println(2*Math.min(count1,count0));
    } main {
        Scanner sc = new Scanner(System.in);
        
        String S = sc.next();
        sc.close();

        int count0 = 0;
        int count1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) == '1')
                count1++;
            if(S.charAt(i) == '0')
                count0++;
        }
        System.out.println(2*Math.min(count1,count0));
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String S = sc.next(); S sc.next() sc.next sc sc.close() sc.close sc int count0 = 0; count0 0 int count1 = 0; count1 0 for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) == '1')
                count1++;
            if(S.charAt(i) == '0')
                count0++;
        } int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
            if(S.charAt(i) == '1')
                count1++;
            if(S.charAt(i) == '0')
                count0++;
        } {
            if(S.charAt(i) == '1')
                count1++;
            if(S.charAt(i) == '0')
                count0++;
        } if(S.charAt(i) == '1')
                count1++; S.charAt(i) == '1' S.charAt(i) S.charAt S i '1' count1++ count1 if(S.charAt(i) == '0')
                count0++; S.charAt(i) == '0' S.charAt(i) S.charAt S i '0' count0++ count0 System.out.println(2*Math.min(count1,count0)) System.out.println System.out System System.out 2*Math.min(count1,count0) 2 Math.min(count1,count0) Math.min Math count1 count0 String args[] args public class Main{

    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        
        String S = sc.next();
        sc.close();

        int count0 = 0;
        int count1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) == '1')
                count1++;
            if(S.charAt(i) == '0')
                count0++;
        }
        System.out.println(2*Math.min(count1,count0));
    }
} public class Main{

    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        
        String S = sc.next();
        sc.close();

        int count0 = 0;
        int count1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) == '1')
                count1++;
            if(S.charAt(i) == '0')
                count0++;
        }
        System.out.println(2*Math.min(count1,count0));
    }
} Main
import java.util.*;

public class Main{

    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        
        String S = sc.next();
        sc.close();

        int count0 = 0;
        int count1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) == '1')
                count1++;
            if(S.charAt(i) == '0')
                count0++;
        }
        System.out.println(2*Math.min(count1,count0));
    }
}