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

int main() {
	string s;
	cin >> s;

	int c0=0, c1=0;
	for (int i = 0;i < s.size();i++) {
		if (s[i] == '0') { c0++; }
		else { c1++; }

	}

	cout << 2 * min(c0, c1) << endl;

}