#include<iostream>
#include<string>

using namespace std;

int main()
{
	string s;
	cin >> s;
	int c1=0,c2=0;
	for(int i=0;i<s.size();i++)
	{
		if(s[i]=='0')
			c1++;
		else
			c2++;
	}
	cout << 2*min(c1,c2) << endl;
}
