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
*/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);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}
static class TaskC   {
public void solve(int testNumber, Scanner in, PrintWriter out) {
        String S = in.next();

        int c0 = 0;
        int c1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) - '0' == 0){
                c0++;
            } else {
                c1++;
            }
        }
        out.println(2 * Math.min(c0, c1));
    }
}
}
 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);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}
static class TaskC   {
public void solve(int testNumber, Scanner in, PrintWriter out) {
        String S = in.next();

        int c0 = 0;
        int c1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) - '0' == 0){
                c0++;
            } else {
                c1++;
            }
        }
        out.println(2 * Math.min(c0, c1));
    }
}
} 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);
		TaskC solver = new TaskC();
		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);
		TaskC solver = new TaskC();
		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) TaskC solver = new TaskC(); solver new TaskC() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class TaskC   {
public void solve(int testNumber, Scanner in, PrintWriter out) {
        String S = in.next();

        int c0 = 0;
        int c1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) - '0' == 0){
                c0++;
            } else {
                c1++;
            }
        }
        out.println(2 * Math.min(c0, c1));
    }
} TaskC public void solve(int testNumber, Scanner in, PrintWriter out) {
        String S = in.next();

        int c0 = 0;
        int c1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) - '0' == 0){
                c0++;
            } else {
                c1++;
            }
        }
        out.println(2 * Math.min(c0, c1));
    } solve {
        String S = in.next();

        int c0 = 0;
        int c1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) - '0' == 0){
                c0++;
            } else {
                c1++;
            }
        }
        out.println(2 * Math.min(c0, c1));
    } String S = in.next(); S in.next() in.next in int c0 = 0; c0 0 int c1 = 0; c1 0 for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) - '0' == 0){
                c0++;
            } else {
                c1++;
            }
        } int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
            if(S.charAt(i) - '0' == 0){
                c0++;
            } else {
                c1++;
            }
        } {
            if(S.charAt(i) - '0' == 0){
                c0++;
            } else {
                c1++;
            }
        } if(S.charAt(i) - '0' == 0){
                c0++;
            } else {
                c1++;
            } S.charAt(i) - '0' == 0 S.charAt(i) - '0' S.charAt(i) S.charAt S i '0' 0 {
                c0++;
            } c0++ c0 {
                c1++;
            } c1++ c1 out.println(2 * Math.min(c0, c1)) out.println out 2 * Math.min(c0, c1) 2 Math.min(c0, c1) Math.min Math c0 c1 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);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}
static class TaskC   {
public void solve(int testNumber, Scanner in, PrintWriter out) {
        String S = in.next();

        int c0 = 0;
        int c1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) - '0' == 0){
                c0++;
            } else {
                c1++;
            }
        }
        out.println(2 * Math.min(c0, c1));
    }
}
} */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);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}
static class TaskC   {
public void solve(int testNumber, Scanner in, PrintWriter out) {
        String S = in.next();

        int c0 = 0;
        int c1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) - '0' == 0){
                c0++;
            } else {
                c1++;
            }
        }
        out.println(2 * Math.min(c0, c1));
    }
}
} 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
*/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);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}
static class TaskC   {
public void solve(int testNumber, Scanner in, PrintWriter out) {
        String S = in.next();

        int c0 = 0;
        int c1 = 0;
        for(int i = 0; i < S.length(); i++){
            if(S.charAt(i) - '0' == 0){
                c0++;
            } else {
                c1++;
            }
        }
        out.println(2 * Math.min(c0, c1));
    }
}
}

