#include<iostream>
#include<string>
using namespace std;
int a=0,b=0;
int main(void)
{
	string s;
	cin>>s;
	for(int i=0;i<s.size();i++)
	{
		if(s[i]=='0')
			a++;
		else
			b++;
	}
	cout<<min(a,b)*2;
	return 0;
}