package main

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

var sc = bufio.NewScanner(os.Stdin)

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

func main() {
	var zero int
	input := line()
	for i := 0; i < len(input); i++ {
		if string(input[i]) == "0" {
			zero++
		}
	}
	fmt.Printf("%d", int(math.Abs(float64(len(input)-zero)))*2)
}
