import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Eric
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        CUnification solver = new CUnification();
        solver.solve(1, in, out);
        out.close();
    }

    static class CUnification {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            char[] arr = s.toCharArray();
            int a = 0;
            int b = 0;
            for (int i = 0; i < arr.length; i++) {
                if (arr[i] == '0')
                    a++;
                else
                    b++;
            }
            out.println(Math.min(a, b) * 2);
        }

    }
}
 import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        CUnification solver = new CUnification();
        solver.solve(1, in, out);
        out.close();
    }

    static class CUnification {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            char[] arr = s.toCharArray();
            int a = 0;
            int b = 0;
            for (int i = 0; i < arr.length; i++) {
                if (arr[i] == '0')
                    a++;
                else
                    b++;
            }
            out.println(Math.min(a, b) * 2);
        }

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        CUnification solver = new CUnification();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        CUnification solver = new CUnification();
        solver.solve(1, in, out);
        out.close();
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out Scanner in = new Scanner(inputStream); in new Scanner(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) CUnification solver = new CUnification(); solver new CUnification() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class CUnification {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            char[] arr = s.toCharArray();
            int a = 0;
            int b = 0;
            for (int i = 0; i < arr.length; i++) {
                if (arr[i] == '0')
                    a++;
                else
                    b++;
            }
            out.println(Math.min(a, b) * 2);
        }

    } CUnification public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            char[] arr = s.toCharArray();
            int a = 0;
            int b = 0;
            for (int i = 0; i < arr.length; i++) {
                if (arr[i] == '0')
                    a++;
                else
                    b++;
            }
            out.println(Math.min(a, b) * 2);
        } solve {
            String s = in.next();
            char[] arr = s.toCharArray();
            int a = 0;
            int b = 0;
            for (int i = 0; i < arr.length; i++) {
                if (arr[i] == '0')
                    a++;
                else
                    b++;
            }
            out.println(Math.min(a, b) * 2);
        } String s = in.next(); s in.next() in.next in char[] arr = s.toCharArray(); arr s.toCharArray() s.toCharArray s int a = 0; a 0 int b = 0; b 0 for (int i = 0; i < arr.length; i++) {
                if (arr[i] == '0')
                    a++;
                else
                    b++;
            } int i = 0; int i = 0; i 0 i < arr.length i arr.length arr arr.length i++ i++ i {
                if (arr[i] == '0')
                    a++;
                else
                    b++;
            } {
                if (arr[i] == '0')
                    a++;
                else
                    b++;
            } if (arr[i] == '0')
                    a++;
                else
                    b++; arr[i] == '0' arr[i] arr i '0' a++ a b++ b out.println(Math.min(a, b) * 2) out.println out Math.min(a, b) * 2 Math.min(a, b) Math.min Math a b 2 int testNumber testNumber Scanner in in PrintWriter out out public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        CUnification solver = new CUnification();
        solver.solve(1, in, out);
        out.close();
    }

    static class CUnification {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            char[] arr = s.toCharArray();
            int a = 0;
            int b = 0;
            for (int i = 0; i < arr.length; i++) {
                if (arr[i] == '0')
                    a++;
                else
                    b++;
            }
            out.println(Math.min(a, b) * 2);
        }

    }
} public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        CUnification solver = new CUnification();
        solver.solve(1, in, out);
        out.close();
    }

    static class CUnification {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            char[] arr = s.toCharArray();
            int a = 0;
            int b = 0;
            for (int i = 0; i < arr.length; i++) {
                if (arr[i] == '0')
                    a++;
                else
                    b++;
            }
            out.println(Math.min(a, b) * 2);
        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Eric
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        CUnification solver = new CUnification();
        solver.solve(1, in, out);
        out.close();
    }

    static class CUnification {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            char[] arr = s.toCharArray();
            int a = 0;
            int b = 0;
            for (int i = 0; i < arr.length; i++) {
                if (arr[i] == '0')
                    a++;
                else
                    b++;
            }
            out.println(Math.min(a, b) * 2);
        }

    }
}

