import java.util.*;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		int n = s.length();
		sc.close();
		int ans = 0;
		for(int i = 0; i < n; ++i) {
			if(s.charAt(i) == '0')++ans;
		}
		if(n - ans < ans)ans = n - ans;
		ans *= 2;
		System.out.println(ans);
	}

}
 import java.util.*; util.* java public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		int n = s.length();
		sc.close();
		int ans = 0;
		for(int i = 0; i < n; ++i) {
			if(s.charAt(i) == '0')++ans;
		}
		if(n - ans < ans)ans = n - ans;
		ans *= 2;
		System.out.println(ans);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		int n = s.length();
		sc.close();
		int ans = 0;
		for(int i = 0; i < n; ++i) {
			if(s.charAt(i) == '0')++ans;
		}
		if(n - ans < ans)ans = n - ans;
		ans *= 2;
		System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		int n = s.length();
		sc.close();
		int ans = 0;
		for(int i = 0; i < n; ++i) {
			if(s.charAt(i) == '0')++ans;
		}
		if(n - ans < ans)ans = n - ans;
		ans *= 2;
		System.out.println(ans);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.next(); s sc.next() sc.next sc int n = s.length(); n s.length() s.length s sc.close() sc.close sc int ans = 0; ans 0 for(int i = 0; i < n; ++i) {
			if(s.charAt(i) == '0')++ans;
		} int i = 0; int i = 0; i 0 i < n i n ++i ++i i {
			if(s.charAt(i) == '0')++ans;
		} {
			if(s.charAt(i) == '0')++ans;
		} if(s.charAt(i) == '0')++ans; s.charAt(i) == '0' s.charAt(i) s.charAt s i '0' ++ans ans if(n - ans < ans)ans = n - ans; n - ans < ans n - ans n ans ans ans = n - ans ans n - ans n ans ans *= 2 ans 2 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		int n = s.length();
		sc.close();
		int ans = 0;
		for(int i = 0; i < n; ++i) {
			if(s.charAt(i) == '0')++ans;
		}
		if(n - ans < ans)ans = n - ans;
		ans *= 2;
		System.out.println(ans);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		int n = s.length();
		sc.close();
		int ans = 0;
		for(int i = 0; i < n; ++i) {
			if(s.charAt(i) == '0')++ans;
		}
		if(n - ans < ans)ans = n - ans;
		ans *= 2;
		System.out.println(ans);
	}

} Main
import java.util.*;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		int n = s.length();
		sc.close();
		int ans = 0;
		for(int i = 0; i < n; ++i) {
			if(s.charAt(i) == '0')++ans;
		}
		if(n - ans < ans)ans = n - ans;
		ans *= 2;
		System.out.println(ans);
	}

}

