#include <iostream>
#include <stdio.h>
#include <string>
#include <algorithm>
#include <cmath>
#include <vector>
#include <functional>
#include <cstdlib>
using namespace std;
#define REP(i,n) for(int i = 0;i < (int)(n);i++)

int main() {
	int n,red=0,blue=0;
	string s;
	cin >> s;
	n = size(s);
	REP(i, n) {
		if (s[i] == '0') {
			red++;
		}
		else {
			blue++;
		}
	}
	cout << min(red, blue) * 2;
	return(0);
}