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

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

	int c0 = 0;
	int c1 = 0;

	for(char c: s){
		if(c=='0') c0++;
		else c1++;
	}

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

	return 0;
}