import java.util.*

fun main(args: Array<String>){
	val cin = Scanner(System.`in`)
    val s = cin.nextLine()

    var z = 0
    var o = 0

    for (i in 0..s.length - 1) {
        if (s[i] == '0') {
            z += 1
        } else {
            o += 1
        }
    }
    if (z > o) {
        println(o*2)
    } else {
        println(z*2)
    }
}