import std.stdio;
import std.string;
import std.conv;
import std.algorithm;
import std.array;
 
void main() {
	auto data = readln().split();
	auto S = data[0].to!string();
	auto first = S;
	auto num = 0;
	foreach (c; S) { if (c == '1') num++; }
	
	writeln(2*min( num, S.length-num ));
}