#include <bits/stdc++.h>
using namespace std;

int main() {
	string s; int a = 0, b = 0;	cin>>s;
	for(int i = 0 ;i<s.length();i++){
		a += s[i] == '1';
		b += s[i] == '0';
	}
	cout<<min(a,b)*2;
	return 0;
}