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