
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.AbstractMap;
import java.util.NoSuchElementException;

/** テンプレート */
public class Main {
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		String S = sc.next();
		//List<Integer> list	= new ArrayList<Integer>();
		int count0 = 0;
		int count1 = 0;


		for(int i = 0; i < S.length(); i++) {
			int num = Character.getNumericValue(S.charAt(i));
			if(num == 0) {
				count0++;
			}else{
				count1++;
			}
		}




		//************************************/
		// ここから出力処理
		//************************************/
		PrintWriter out = new PrintWriter(System.out);

		if(count0 < count1) {
			out.println(count0*2);
		}else {
			out.println(count1*2);
		}

		// 最後に必ずFlush
		out.flush();
	}

//	static int calc(List<Integer> list, int count) {
//		final int DELETED = -100;
//		int prev = DELETED;
//		int tmpCount = 0;
//
//		for(int i = 0; i < list.size(); i++) {
//			int corrent = list.get(i);
//
//			if(prev == DELETED || corrent == DELETED) {
//				prev = corrent;
//				continue;
//			}
//
//			if(prev + corrent == 1) {
//				tmpCount++; // あとで2かけること
//				list.set(i, DELETED);
//				list.set(i-1, DELETED);
//				prev = DELETED;
//				continue;
//			}
//
//			prev = corrent;
//		}
//
//		list = rmList(list);
//
//		if(tmpCount > 0) {
//			count += tmpCount;
//			count = calc(list, count);
//		}
//
//		return count;
//	}
//
//	static List<Integer> rmList(List<Integer> list) {
//		Iterator<Integer> it = list.iterator();
//
//		while(it.hasNext()) {
//			if (it.next() == -100){
//				it.remove();
//			}
//		}
//		return list;
//	}



}

///** テンプレート */
//public class Main {
//	public static void main(String[] args) {
//		FastScanner sc = new FastScanner();
//		int N = sc.nextInt();
//		int M =  sc.nextInt();
//
//		int[] ary = new int[N];
//		for(int i = 0; i < N; i++) {
//			ary[i] = sc.nextInt();
//		}
//
//		//************************************/
//		// ここから出力処理
//		//************************************/
//		PrintWriter out = new PrintWriter(System.out);
//
//
//		out.println("hoge");
//
//		// 最後に必ずFlush
//		out.flush();
//	}
//}

/** スキャン用 */
class FastScanner {
	private final InputStream in = System.in;
	private final byte[] buffer = new byte[1024];
	private int ptr = 0;
	private int buflen = 0;

	/** クラス内部用だよ */
	private boolean hasNextByte() {
		if (ptr < buflen) {
			return true;
		} else {
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		}
		return true;
	}

	/** クラス内部用だよ */
	private int readByte() {
		if (hasNextByte()) {
			return buffer[ptr++];
		} else {
			return -1;
		}
	}

	/**
	 * クラス内部用だよ
	 * ASCII の文字の内、表示用の文字を返す関数
	 *
	 * @return 改行とか制御文字じゃない、表示用文字ならtrue
	 * */
	private static boolean isPrintableChar(int c) {
		return 33 <= c && c <= 126;
	}

	/**
	 * @return 改行文字とか空白以外を除いた、次の文字があればtrue
	 * */
	public boolean hasNext() {
		while (hasNextByte() && !isPrintableChar(buffer[ptr])) {
			ptr++;
		}
		return hasNextByte();
	}

	/**
	 *
	 * @return 次の文字列
	 */
	public String next() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}

		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while (isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}

	/**
	 *
	 * @return 次のLong
	 */
	public long nextLong() {
		if (!hasNext())
			throw new NoSuchElementException();
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while (true) {
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			} else if (b == -1 || !isPrintableChar(b)) {
				return minus ? -n : n;
			} else {
				throw new NumberFormatException();
			}
			b = readByte();
		}
	}

	/**
	 *
	 * @return 次のInt
	 */
	public int nextInt() {
		long nl = nextLong();
		if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
			throw new NumberFormatException();
		return (int) nl;
	}

	/**
	 *
	 * @return 次のDouble
	 */
	public double nextDouble() {
		return Double.parseDouble(next());
	}
}

class Pair<K, V> extends AbstractMap.SimpleEntry<K, V> {
	/** serialVersionUID. */
	private static final long serialVersionUID = 6411527075103472113L;

	public Pair(final K key, final V value) {
		super(key, value);
	}
} import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.AbstractMap; AbstractMap java.util import java.util.NoSuchElementException; NoSuchElementException java.util public class Main {
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		String S = sc.next();
		//List<Integer> list	= new ArrayList<Integer>();
		int count0 = 0;
		int count1 = 0;


		for(int i = 0; i < S.length(); i++) {
			int num = Character.getNumericValue(S.charAt(i));
			if(num == 0) {
				count0++;
			}else{
				count1++;
			}
		}




		//************************************/
		// ここから出力処理
		//************************************/
		PrintWriter out = new PrintWriter(System.out);

		if(count0 < count1) {
			out.println(count0*2);
		}else {
			out.println(count1*2);
		}

		// 最後に必ずFlush
		out.flush();
	}

//	static int calc(List<Integer> list, int count) {
//		final int DELETED = -100;
//		int prev = DELETED;
//		int tmpCount = 0;
//
//		for(int i = 0; i < list.size(); i++) {
//			int corrent = list.get(i);
//
//			if(prev == DELETED || corrent == DELETED) {
//				prev = corrent;
//				continue;
//			}
//
//			if(prev + corrent == 1) {
//				tmpCount++; // あとで2かけること
//				list.set(i, DELETED);
//				list.set(i-1, DELETED);
//				prev = DELETED;
//				continue;
//			}
//
//			prev = corrent;
//		}
//
//		list = rmList(list);
//
//		if(tmpCount > 0) {
//			count += tmpCount;
//			count = calc(list, count);
//		}
//
//		return count;
//	}
//
//	static List<Integer> rmList(List<Integer> list) {
//		Iterator<Integer> it = list.iterator();
//
//		while(it.hasNext()) {
//			if (it.next() == -100){
//				it.remove();
//			}
//		}
//		return list;
//	}



} Main public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		String S = sc.next();
		//List<Integer> list	= new ArrayList<Integer>();
		int count0 = 0;
		int count1 = 0;


		for(int i = 0; i < S.length(); i++) {
			int num = Character.getNumericValue(S.charAt(i));
			if(num == 0) {
				count0++;
			}else{
				count1++;
			}
		}




		//************************************/
		// ここから出力処理
		//************************************/
		PrintWriter out = new PrintWriter(System.out);

		if(count0 < count1) {
			out.println(count0*2);
		}else {
			out.println(count1*2);
		}

		// 最後に必ずFlush
		out.flush();
	} main {
		FastScanner sc = new FastScanner();
		String S = sc.next();
		//List<Integer> list	= new ArrayList<Integer>();
		int count0 = 0;
		int count1 = 0;


		for(int i = 0; i < S.length(); i++) {
			int num = Character.getNumericValue(S.charAt(i));
			if(num == 0) {
				count0++;
			}else{
				count1++;
			}
		}




		//************************************/
		// ここから出力処理
		//************************************/
		PrintWriter out = new PrintWriter(System.out);

		if(count0 < count1) {
			out.println(count0*2);
		}else {
			out.println(count1*2);
		}

		// 最後に必ずFlush
		out.flush();
	} FastScanner sc = new FastScanner(); sc new FastScanner() String S = sc.next(); S sc.next() sc.next sc int count0 = 0; count0 0 int count1 = 0; count1 0 for(int i = 0; i < S.length(); i++) {
			int num = Character.getNumericValue(S.charAt(i));
			if(num == 0) {
				count0++;
			}else{
				count1++;
			}
		} int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
			int num = Character.getNumericValue(S.charAt(i));
			if(num == 0) {
				count0++;
			}else{
				count1++;
			}
		} {
			int num = Character.getNumericValue(S.charAt(i));
			if(num == 0) {
				count0++;
			}else{
				count1++;
			}
		} int num = Character.getNumericValue(S.charAt(i)); num Character.getNumericValue(S.charAt(i)) Character.getNumericValue Character S.charAt(i) S.charAt S i if(num == 0) {
				count0++;
			}else{
				count1++;
			} num == 0 num 0 {
				count0++;
			} count0++ count0 {
				count1++;
			} count1++ count1 PrintWriter out = new PrintWriter(System.out); out new PrintWriter(System.out) if(count0 < count1) {
			out.println(count0*2);
		}else {
			out.println(count1*2);
		} count0 < count1 count0 count1 {
			out.println(count0*2);
		} out.println(count0*2) out.println out count0*2 count0 2 {
			out.println(count1*2);
		} out.println(count1*2) out.println out count1*2 count1 2 out.flush() out.flush out String[] args args class FastScanner {
	private final InputStream in = System.in;
	private final byte[] buffer = new byte[1024];
	private int ptr = 0;
	private int buflen = 0;

	/** クラス内部用だよ */
	private boolean hasNextByte() {
		if (ptr < buflen) {
			return true;
		} else {
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		}
		return true;
	}

	/** クラス内部用だよ */
	private int readByte() {
		if (hasNextByte()) {
			return buffer[ptr++];
		} else {
			return -1;
		}
	}

	/**
	 * クラス内部用だよ
	 * ASCII の文字の内、表示用の文字を返す関数
	 *
	 * @return 改行とか制御文字じゃない、表示用文字ならtrue
	 * */
	private static boolean isPrintableChar(int c) {
		return 33 <= c && c <= 126;
	}

	/**
	 * @return 改行文字とか空白以外を除いた、次の文字があればtrue
	 * */
	public boolean hasNext() {
		while (hasNextByte() && !isPrintableChar(buffer[ptr])) {
			ptr++;
		}
		return hasNextByte();
	}

	/**
	 *
	 * @return 次の文字列
	 */
	public String next() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}

		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while (isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}

	/**
	 *
	 * @return 次のLong
	 */
	public long nextLong() {
		if (!hasNext())
			throw new NoSuchElementException();
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while (true) {
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			} else if (b == -1 || !isPrintableChar(b)) {
				return minus ? -n : n;
			} else {
				throw new NumberFormatException();
			}
			b = readByte();
		}
	}

	/**
	 *
	 * @return 次のInt
	 */
	public int nextInt() {
		long nl = nextLong();
		if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
			throw new NumberFormatException();
		return (int) nl;
	}

	/**
	 *
	 * @return 次のDouble
	 */
	public double nextDouble() {
		return Double.parseDouble(next());
	}
} FastScanner private final InputStream in = System.in; in System.in System System.in private final byte[] buffer = new byte[1024]; buffer new byte[1024] 1024 private int ptr = 0; ptr 0 private int buflen = 0; buflen 0 /** クラス内部用だよ */
	private boolean hasNextByte() {
		if (ptr < buflen) {
			return true;
		} else {
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		}
		return true;
	} hasNextByte {
		if (ptr < buflen) {
			return true;
		} else {
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		}
		return true;
	} if (ptr < buflen) {
			return true;
		} else {
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		} ptr < buflen ptr buflen {
			return true;
		} return true; true {
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		} ptr = 0 ptr 0 try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			} catch (IOException e) {
				e.printStackTrace();
			} IOException e {
				e.printStackTrace();
			} e.printStackTrace() e.printStackTrace e {
				buflen = in.read(buffer);
			} buflen = in.read(buffer) buflen in.read(buffer) in.read in buffer if (buflen <= 0) {
				return false;
			} buflen <= 0 buflen 0 {
				return false;
			} return false; false return true; true /** クラス内部用だよ */
	private int readByte() {
		if (hasNextByte()) {
			return buffer[ptr++];
		} else {
			return -1;
		}
	} readByte {
		if (hasNextByte()) {
			return buffer[ptr++];
		} else {
			return -1;
		}
	} if (hasNextByte()) {
			return buffer[ptr++];
		} else {
			return -1;
		} hasNextByte() hasNextByte {
			return buffer[ptr++];
		} return buffer[ptr++]; buffer[ptr++] buffer ptr++ ptr {
			return -1;
		} return -1; -1 1 /**
	 * クラス内部用だよ
	 * ASCII の文字の内、表示用の文字を返す関数
	 *
	 * @return 改行とか制御文字じゃない、表示用文字ならtrue
	 * */
	private static boolean isPrintableChar(int c) {
		return 33 <= c && c <= 126;
	} isPrintableChar {
		return 33 <= c && c <= 126;
	} return 33 <= c && c <= 126; 33 <= c && c <= 126 33 <= c 33 c c <= 126 c 126 int c c /**
	 * @return 改行文字とか空白以外を除いた、次の文字があればtrue
	 * */
	public boolean hasNext() {
		while (hasNextByte() && !isPrintableChar(buffer[ptr])) {
			ptr++;
		}
		return hasNextByte();
	} hasNext {
		while (hasNextByte() && !isPrintableChar(buffer[ptr])) {
			ptr++;
		}
		return hasNextByte();
	} while (hasNextByte() && !isPrintableChar(buffer[ptr])) {
			ptr++;
		} hasNextByte() && !isPrintableChar(buffer[ptr]) hasNextByte() hasNextByte !isPrintableChar(buffer[ptr]) isPrintableChar(buffer[ptr]) isPrintableChar buffer[ptr] buffer ptr {
			ptr++;
		} ptr++ ptr return hasNextByte(); hasNextByte() hasNextByte /**
	 *
	 * @return 次の文字列
	 */
	public String next() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}

		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while (isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	} next {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}

		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while (isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	} if (!hasNext()) {
			throw new NoSuchElementException();
		} !hasNext() hasNext() hasNext {
			throw new NoSuchElementException();
		} throw new NoSuchElementException(); new NoSuchElementException() StringBuilder sb = new StringBuilder(); sb new StringBuilder() int b = readByte(); b readByte() readByte while (isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		} isPrintableChar(b) isPrintableChar b {
			sb.appendCodePoint(b);
			b = readByte();
		} sb.appendCodePoint(b) sb.appendCodePoint sb b b = readByte() b readByte() readByte return sb.toString(); sb.toString() sb.toString sb /**
	 *
	 * @return 次のLong
	 */
	public long nextLong() {
		if (!hasNext())
			throw new NoSuchElementException();
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while (true) {
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			} else if (b == -1 || !isPrintableChar(b)) {
				return minus ? -n : n;
			} else {
				throw new NumberFormatException();
			}
			b = readByte();
		}
	} nextLong {
		if (!hasNext())
			throw new NoSuchElementException();
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while (true) {
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			} else if (b == -1 || !isPrintableChar(b)) {
				return minus ? -n : n;
			} else {
				throw new NumberFormatException();
			}
			b = readByte();
		}
	} if (!hasNext())
			throw new NoSuchElementException(); !hasNext() hasNext() hasNext throw new NoSuchElementException(); new NoSuchElementException() long n = 0; n 0 boolean minus = false; minus false int b = readByte(); b readByte() readByte if (b == '-') {
			minus = true;
			b = readByte();
		} b == '-' b '-' {
			minus = true;
			b = readByte();
		} minus = true minus true b = readByte() b readByte() readByte if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		} b < '0' || '9' < b b < '0' b '0' '9' < b '9' b {
			throw new NumberFormatException();
		} throw new NumberFormatException(); new NumberFormatException() while (true) {
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			} else if (b == -1 || !isPrintableChar(b)) {
				return minus ? -n : n;
			} else {
				throw new NumberFormatException();
			}
			b = readByte();
		} true {
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			} else if (b == -1 || !isPrintableChar(b)) {
				return minus ? -n : n;
			} else {
				throw new NumberFormatException();
			}
			b = readByte();
		} if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			} else if (b == -1 || !isPrintableChar(b)) {
				return minus ? -n : n;
			} else {
				throw new NumberFormatException();
			} '0' <= b && b <= '9' '0' <= b '0' b b <= '9' b '9' {
				n *= 10;
				n += b - '0';
			} n *= 10 n 10 n += b - '0' n b - '0' b '0' if (b == -1 || !isPrintableChar(b)) {
				return minus ? -n : n;
			} else {
				throw new NumberFormatException();
			} b == -1 || !isPrintableChar(b) b == -1 b -1 1 !isPrintableChar(b) isPrintableChar(b) isPrintableChar b {
				return minus ? -n : n;
			} return minus ? -n : n; minus ? -n : n minus -n n n {
				throw new NumberFormatException();
			} throw new NumberFormatException(); new NumberFormatException() b = readByte() b readByte() readByte /**
	 *
	 * @return 次のInt
	 */
	public int nextInt() {
		long nl = nextLong();
		if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
			throw new NumberFormatException();
		return (int) nl;
	} nextInt {
		long nl = nextLong();
		if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
			throw new NumberFormatException();
		return (int) nl;
	} long nl = nextLong(); nl nextLong() nextLong if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
			throw new NumberFormatException(); nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE nl < Integer.MIN_VALUE nl Integer.MIN_VALUE Integer Integer.MIN_VALUE nl > Integer.MAX_VALUE nl Integer.MAX_VALUE Integer Integer.MAX_VALUE throw new NumberFormatException(); new NumberFormatException() return (int) nl; (int) nl /**
	 *
	 * @return 次のDouble
	 */
	public double nextDouble() {
		return Double.parseDouble(next());
	} nextDouble {
		return Double.parseDouble(next());
	} return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next class Pair<K, V> extends AbstractMap.SimpleEntry<K, V> {
	/** serialVersionUID. */
	private static final long serialVersionUID = 6411527075103472113L;

	public Pair(final K key, final V value) {
		super(key, value);
	}
} Pair /** serialVersionUID. */
	private static final long serialVersionUID = 6411527075103472113L; serialVersionUID 6411527075103472113L public Pair(final K key, final V value) {
		super(key, value);
	} Pair {
		super(key, value);
	} super(key, value) super key value final K key key final V value value SimpleEntry public class Main {
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		String S = sc.next();
		//List<Integer> list	= new ArrayList<Integer>();
		int count0 = 0;
		int count1 = 0;


		for(int i = 0; i < S.length(); i++) {
			int num = Character.getNumericValue(S.charAt(i));
			if(num == 0) {
				count0++;
			}else{
				count1++;
			}
		}




		//************************************/
		// ここから出力処理
		//************************************/
		PrintWriter out = new PrintWriter(System.out);

		if(count0 < count1) {
			out.println(count0*2);
		}else {
			out.println(count1*2);
		}

		// 最後に必ずFlush
		out.flush();
	}

//	static int calc(List<Integer> list, int count) {
//		final int DELETED = -100;
//		int prev = DELETED;
//		int tmpCount = 0;
//
//		for(int i = 0; i < list.size(); i++) {
//			int corrent = list.get(i);
//
//			if(prev == DELETED || corrent == DELETED) {
//				prev = corrent;
//				continue;
//			}
//
//			if(prev + corrent == 1) {
//				tmpCount++; // あとで2かけること
//				list.set(i, DELETED);
//				list.set(i-1, DELETED);
//				prev = DELETED;
//				continue;
//			}
//
//			prev = corrent;
//		}
//
//		list = rmList(list);
//
//		if(tmpCount > 0) {
//			count += tmpCount;
//			count = calc(list, count);
//		}
//
//		return count;
//	}
//
//	static List<Integer> rmList(List<Integer> list) {
//		Iterator<Integer> it = list.iterator();
//
//		while(it.hasNext()) {
//			if (it.next() == -100){
//				it.remove();
//			}
//		}
//		return list;
//	}



} public class Main {
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		String S = sc.next();
		//List<Integer> list	= new ArrayList<Integer>();
		int count0 = 0;
		int count1 = 0;


		for(int i = 0; i < S.length(); i++) {
			int num = Character.getNumericValue(S.charAt(i));
			if(num == 0) {
				count0++;
			}else{
				count1++;
			}
		}




		//************************************/
		// ここから出力処理
		//************************************/
		PrintWriter out = new PrintWriter(System.out);

		if(count0 < count1) {
			out.println(count0*2);
		}else {
			out.println(count1*2);
		}

		// 最後に必ずFlush
		out.flush();
	}

//	static int calc(List<Integer> list, int count) {
//		final int DELETED = -100;
//		int prev = DELETED;
//		int tmpCount = 0;
//
//		for(int i = 0; i < list.size(); i++) {
//			int corrent = list.get(i);
//
//			if(prev == DELETED || corrent == DELETED) {
//				prev = corrent;
//				continue;
//			}
//
//			if(prev + corrent == 1) {
//				tmpCount++; // あとで2かけること
//				list.set(i, DELETED);
//				list.set(i-1, DELETED);
//				prev = DELETED;
//				continue;
//			}
//
//			prev = corrent;
//		}
//
//		list = rmList(list);
//
//		if(tmpCount > 0) {
//			count += tmpCount;
//			count = calc(list, count);
//		}
//
//		return count;
//	}
//
//	static List<Integer> rmList(List<Integer> list) {
//		Iterator<Integer> it = list.iterator();
//
//		while(it.hasNext()) {
//			if (it.next() == -100){
//				it.remove();
//			}
//		}
//		return list;
//	}



} Main

import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.AbstractMap;
import java.util.NoSuchElementException;

/** テンプレート */
public class Main {
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		String S = sc.next();
		//List<Integer> list	= new ArrayList<Integer>();
		int count0 = 0;
		int count1 = 0;


		for(int i = 0; i < S.length(); i++) {
			int num = Character.getNumericValue(S.charAt(i));
			if(num == 0) {
				count0++;
			}else{
				count1++;
			}
		}




		//************************************/
		// ここから出力処理
		//************************************/
		PrintWriter out = new PrintWriter(System.out);

		if(count0 < count1) {
			out.println(count0*2);
		}else {
			out.println(count1*2);
		}

		// 最後に必ずFlush
		out.flush();
	}

//	static int calc(List<Integer> list, int count) {
//		final int DELETED = -100;
//		int prev = DELETED;
//		int tmpCount = 0;
//
//		for(int i = 0; i < list.size(); i++) {
//			int corrent = list.get(i);
//
//			if(prev == DELETED || corrent == DELETED) {
//				prev = corrent;
//				continue;
//			}
//
//			if(prev + corrent == 1) {
//				tmpCount++; // あとで2かけること
//				list.set(i, DELETED);
//				list.set(i-1, DELETED);
//				prev = DELETED;
//				continue;
//			}
//
//			prev = corrent;
//		}
//
//		list = rmList(list);
//
//		if(tmpCount > 0) {
//			count += tmpCount;
//			count = calc(list, count);
//		}
//
//		return count;
//	}
//
//	static List<Integer> rmList(List<Integer> list) {
//		Iterator<Integer> it = list.iterator();
//
//		while(it.hasNext()) {
//			if (it.next() == -100){
//				it.remove();
//			}
//		}
//		return list;
//	}



}

///** テンプレート */
//public class Main {
//	public static void main(String[] args) {
//		FastScanner sc = new FastScanner();
//		int N = sc.nextInt();
//		int M =  sc.nextInt();
//
//		int[] ary = new int[N];
//		for(int i = 0; i < N; i++) {
//			ary[i] = sc.nextInt();
//		}
//
//		//************************************/
//		// ここから出力処理
//		//************************************/
//		PrintWriter out = new PrintWriter(System.out);
//
//
//		out.println("hoge");
//
//		// 最後に必ずFlush
//		out.flush();
//	}
//}

/** スキャン用 */
class FastScanner {
	private final InputStream in = System.in;
	private final byte[] buffer = new byte[1024];
	private int ptr = 0;
	private int buflen = 0;

	/** クラス内部用だよ */
	private boolean hasNextByte() {
		if (ptr < buflen) {
			return true;
		} else {
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		}
		return true;
	}

	/** クラス内部用だよ */
	private int readByte() {
		if (hasNextByte()) {
			return buffer[ptr++];
		} else {
			return -1;
		}
	}

	/**
	 * クラス内部用だよ
	 * ASCII の文字の内、表示用の文字を返す関数
	 *
	 * @return 改行とか制御文字じゃない、表示用文字ならtrue
	 * */
	private static boolean isPrintableChar(int c) {
		return 33 <= c && c <= 126;
	}

	/**
	 * @return 改行文字とか空白以外を除いた、次の文字があればtrue
	 * */
	public boolean hasNext() {
		while (hasNextByte() && !isPrintableChar(buffer[ptr])) {
			ptr++;
		}
		return hasNextByte();
	}

	/**
	 *
	 * @return 次の文字列
	 */
	public String next() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}

		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while (isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}

	/**
	 *
	 * @return 次のLong
	 */
	public long nextLong() {
		if (!hasNext())
			throw new NoSuchElementException();
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while (true) {
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			} else if (b == -1 || !isPrintableChar(b)) {
				return minus ? -n : n;
			} else {
				throw new NumberFormatException();
			}
			b = readByte();
		}
	}

	/**
	 *
	 * @return 次のInt
	 */
	public int nextInt() {
		long nl = nextLong();
		if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
			throw new NumberFormatException();
		return (int) nl;
	}

	/**
	 *
	 * @return 次のDouble
	 */
	public double nextDouble() {
		return Double.parseDouble(next());
	}
}

class Pair<K, V> extends AbstractMap.SimpleEntry<K, V> {
	/** serialVersionUID. */
	private static final long serialVersionUID = 6411527075103472113L;

	public Pair(final K key, final V value) {
		super(key, value);
	}
}
