import java.util.*;
import java.io.*;

public class Main{


    public static void main(String[] args) {
        FastReader in = new FastReader();

        String s = in.nextLine();
        int cnt[] = new int[2];
        for (int l = 0; l < s.length(); ++l){
            cnt[(int)s.charAt(l) - (int)'0'] ++;
        }
        System.out.println(Math.min(cnt[0], cnt[1])*2);




    }

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
} import java.util.*; util.* java import java.io.*; io.* java public class Main{


    public static void main(String[] args) {
        FastReader in = new FastReader();

        String s = in.nextLine();
        int cnt[] = new int[2];
        for (int l = 0; l < s.length(); ++l){
            cnt[(int)s.charAt(l) - (int)'0'] ++;
        }
        System.out.println(Math.min(cnt[0], cnt[1])*2);




    }

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
} Main public static void main(String[] args) {
        FastReader in = new FastReader();

        String s = in.nextLine();
        int cnt[] = new int[2];
        for (int l = 0; l < s.length(); ++l){
            cnt[(int)s.charAt(l) - (int)'0'] ++;
        }
        System.out.println(Math.min(cnt[0], cnt[1])*2);




    } main {
        FastReader in = new FastReader();

        String s = in.nextLine();
        int cnt[] = new int[2];
        for (int l = 0; l < s.length(); ++l){
            cnt[(int)s.charAt(l) - (int)'0'] ++;
        }
        System.out.println(Math.min(cnt[0], cnt[1])*2);




    } FastReader in = new FastReader(); in new FastReader() String s = in.nextLine(); s in.nextLine() in.nextLine in int cnt[] = new int[2]; cnt new int[2] 2 for (int l = 0; l < s.length(); ++l){
            cnt[(int)s.charAt(l) - (int)'0'] ++;
        } int l = 0; int l = 0; l 0 l < s.length() l s.length() s.length s ++l ++l l {
            cnt[(int)s.charAt(l) - (int)'0'] ++;
        } {
            cnt[(int)s.charAt(l) - (int)'0'] ++;
        } cnt[(int)s.charAt(l) - (int)'0'] ++ cnt[(int)s.charAt(l) - (int)'0'] cnt (int)s.charAt(l) - (int)'0' (int)s.charAt(l) s.charAt s l (int)'0' System.out.println(Math.min(cnt[0], cnt[1])*2) System.out.println System.out System System.out Math.min(cnt[0], cnt[1])*2 Math.min(cnt[0], cnt[1]) Math.min Math cnt[0] cnt 0 cnt[1] cnt 1 2 String[] args args static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    } FastReader BufferedReader br; br StringTokenizer st; st public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        } FastReader {
            br = new BufferedReader(new InputStreamReader(System.in));
        } br = new BufferedReader(new InputStreamReader(System.in)) br new BufferedReader(new InputStreamReader(System.in)) String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        } next {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        } while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } st == null || !st.hasMoreElements() st == null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                } IOException e {
                    e.printStackTrace();
                } e.printStackTrace() e.printStackTrace e {
                    st = new StringTokenizer(br.readLine());
                } st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int nextInt() {
            return Integer.parseInt(next());
        } nextInt {
            return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next long nextLong() {
            return Long.parseLong(next());
        } nextLong {
            return Long.parseLong(next());
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next double nextDouble() {
            return Double.parseDouble(next());
        } nextDouble {
            return Double.parseDouble(next());
        } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        } nextLine {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        } String str = ""; str "" try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } IOException e {
                e.printStackTrace();
            } e.printStackTrace() e.printStackTrace e {
                str = br.readLine();
            } str = br.readLine() str br.readLine() br.readLine br return str; str public class Main{


    public static void main(String[] args) {
        FastReader in = new FastReader();

        String s = in.nextLine();
        int cnt[] = new int[2];
        for (int l = 0; l < s.length(); ++l){
            cnt[(int)s.charAt(l) - (int)'0'] ++;
        }
        System.out.println(Math.min(cnt[0], cnt[1])*2);




    }

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
} public class Main{


    public static void main(String[] args) {
        FastReader in = new FastReader();

        String s = in.nextLine();
        int cnt[] = new int[2];
        for (int l = 0; l < s.length(); ++l){
            cnt[(int)s.charAt(l) - (int)'0'] ++;
        }
        System.out.println(Math.min(cnt[0], cnt[1])*2);




    }

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
} Main
import java.util.*;
import java.io.*;

public class Main{


    public static void main(String[] args) {
        FastReader in = new FastReader();

        String s = in.nextLine();
        int cnt[] = new int[2];
        for (int l = 0; l < s.length(); ++l){
            cnt[(int)s.charAt(l) - (int)'0'] ++;
        }
        System.out.println(Math.min(cnt[0], cnt[1])*2);




    }

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
}