package main

import (
	"bufio"
	"fmt"
	"os"
)

var sc = bufio.NewScanner(os.Stdin)

func nextLine() string {
	sc.Scan()
	return sc.Text()
}

func main() {
	s := nextLine()

	z := 0
	o := 0
	for _, r := range s {
		if r == '0' {
			z++
		} else {
			o++
		}
	}

	if z < o {
		fmt.Println(z * 2)
	} else {
		fmt.Println(o * 2)
	}
}
