import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Vector;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Stack;
import java.io.InputStream;

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

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            String x = in.next();
            Stack<Character> s = new Stack<>();
            int c = 0;
            for (int i = 0; i < x.length(); i++) {
                s.push(x.charAt(i));
                while (s.size() > 1) {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                }
            }
            out.println(c * 2);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

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

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            String x = in.next();
            Stack<Character> s = new Stack<>();
            int c = 0;
            for (int i = 0; i < x.length(); i++) {
                s.push(x.charAt(i));
                while (s.size() > 1) {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                }
            }
            out.println(c * 2);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        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 InputReader in = new InputReader(inputStream); in new InputReader(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) TaskB solver = new TaskB(); solver new TaskB() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            String x = in.next();
            Stack<Character> s = new Stack<>();
            int c = 0;
            for (int i = 0; i < x.length(); i++) {
                s.push(x.charAt(i));
                while (s.size() > 1) {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                }
            }
            out.println(c * 2);
        }

    } TaskB public void solve(int testNumber, InputReader in, PrintWriter out) {
            String x = in.next();
            Stack<Character> s = new Stack<>();
            int c = 0;
            for (int i = 0; i < x.length(); i++) {
                s.push(x.charAt(i));
                while (s.size() > 1) {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                }
            }
            out.println(c * 2);
        } solve {
            String x = in.next();
            Stack<Character> s = new Stack<>();
            int c = 0;
            for (int i = 0; i < x.length(); i++) {
                s.push(x.charAt(i));
                while (s.size() > 1) {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                }
            }
            out.println(c * 2);
        } String x = in.next(); x in.next() in.next in Stack<Character> s = new Stack<>(); s new Stack<>() int c = 0; c 0 for (int i = 0; i < x.length(); i++) {
                s.push(x.charAt(i));
                while (s.size() > 1) {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                }
            } int i = 0; int i = 0; i 0 i < x.length() i x.length() x.length x i++ i++ i {
                s.push(x.charAt(i));
                while (s.size() > 1) {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                }
            } {
                s.push(x.charAt(i));
                while (s.size() > 1) {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                }
            } s.push(x.charAt(i)) s.push s x.charAt(i) x.charAt x i while (s.size() > 1) {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                } s.size() > 1 s.size() s.size s 1 {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                } Character p = s.pop(); p s.pop() s.pop s Character q = s.pop(); q s.pop() s.pop s if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    } (p == '1' && q == '0') || (p == '0' && q == '1') (p == '1' && q == '0') p == '1' p '1' q == '0' q '0' (p == '0' && q == '1') p == '0' p '0' q == '1' q '1' {
                        c++;
                        continue;
                    } c++ c continue; {
                        s.push(q);
                        s.push(p);
                        break;
                    } s.push(q) s.push s q s.push(p) s.push s p break; out.println(c * 2) out.println out c * 2 c 2 int testNumber testNumber InputReader in in PrintWriter out out static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

    } InputReader public BufferedReader reader; reader public StringTokenizer tokenizer; tokenizer public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        } InputReader {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        } reader = new BufferedReader(new InputStreamReader(stream), 32768) reader new BufferedReader(new InputStreamReader(stream), 32768) tokenizer = null tokenizer null InputStream stream stream public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } next {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } IOException e {
                    throw new RuntimeException(e);
                } throw new RuntimeException(e); new RuntimeException(e) {
                    tokenizer = new StringTokenizer(reader.readLine());
                } tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return tokenizer.nextToken(); tokenizer.nextToken() tokenizer.nextToken tokenizer public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            String x = in.next();
            Stack<Character> s = new Stack<>();
            int c = 0;
            for (int i = 0; i < x.length(); i++) {
                s.push(x.charAt(i));
                while (s.size() > 1) {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                }
            }
            out.println(c * 2);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

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

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            String x = in.next();
            Stack<Character> s = new Stack<>();
            int c = 0;
            for (int i = 0; i < x.length(); i++) {
                s.push(x.charAt(i));
                while (s.size() > 1) {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                }
            }
            out.println(c * 2);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Vector;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Stack;
import java.io.InputStream;

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

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            String x = in.next();
            Stack<Character> s = new Stack<>();
            int c = 0;
            for (int i = 0; i < x.length(); i++) {
                s.push(x.charAt(i));
                while (s.size() > 1) {
                    Character p = s.pop();
                    Character q = s.pop();
                    if ((p == '1' && q == '0') || (p == '0' && q == '1')) {
                        c++;
                        continue;
                    } else {
                        s.push(q);
                        s.push(p);
                        break;
                    }
                }
            }
            out.println(c * 2);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

    }
}

