
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);
	}
}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz