
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		//		new Main().solveA();
		//		new Main().solveB();
		new Main().solveC();
		// new Main().solveD();
	}

	private void solveA() {
		Scanner scanner = null;
		int numA = 0;
		int numB = 0;
		int numC = 0;

		try {
			scanner = new Scanner(System.in);
			numA = scanner.nextInt();
			numB = scanner.nextInt();
			numC = scanner.nextInt();

			int wk = numB;
			int res = 0;
			while (wk >= numA && res < numC) {
				wk -= numA;
				res++;
			}

			System.out.println(res);

		} finally {
			if (scanner != null) {
				scanner.close();
			}
		}
	}

	private void solveB() {
		Scanner scanner = null;
		int numA = 0;
		int numB = 0;
		int numK = 0;

		try {
			scanner = new Scanner(System.in);
			numA = scanner.nextInt();
			numB = scanner.nextInt();
			numK = scanner.nextInt();

			List<Integer> wk = new ArrayList<Integer>();
			for (int i = 1; i <= Math.max(numA, numB); i++) {
				if (numA % i == 0 && numB % i == 0) {
					wk.add(i);
				}
			}

			System.out.println(wk.get(wk.size() - 1 - numK));

		} finally {
			if (scanner != null) {
				scanner.close();
			}
		}
	}

	private int getList(List<Character> wk) {

		if (wk.size() < 2) {
			return 0;
		}

		int res = 0;
		int i1 = 0;
		int i2 = 1;
		for (int i = 1; i < wk.size(); i++) {
			if (wk.get(i) != wk.get(i - 1)) {
				i1 = i - 1;
				i2 = i;
				break;
			}
			if (i == wk.size() - 1) {
				return 0;
			}
		}
		while (i2 < wk.size()) {

			char c1 = wk.get(i1);
			char c2 = wk.get(i2);
			if (c1 != c2) {
				wk.remove(i2);
				wk.remove(i1);
				res += 2;
			} else {
				i1 = i2;
				i2 = i2 + 1;
			}
		}
		return getList(wk) + res;
	}

	private void solveC() {
		Scanner scanner = null;
		char[] wkS;

		try {
			scanner = new Scanner(System.in);
			wkS = scanner.next().toCharArray();

			List<Character> wk = new ArrayList<Character>();
			for (char c : wkS) {
				wk.add(c);
			}

			System.out.println(getList(wk));

		} finally {
			if (scanner != null) {
				scanner.close();
			}
		}
	}

	private void solveD() {
		Scanner scanner = null;
		int numN = 0;
		int numK = 0;
		int numS = 0;

		try {
			scanner = new Scanner(System.in);
			numN = scanner.nextInt();

			System.out.println("");

		} finally {
			if (scanner != null) {
				scanner.close();
			}
		}
	}
}