#include <iostream>
#include <sstream>
#include <vector>
#include <cmath>
#include <ctime>
#include <cassert>
#include <iomanip>
#include <vector>
#include <cstdio>
#include <float.h>
#include <queue>
#include <set>
#include <map>
#include <fstream>
#include <cstdlib>
#include <string>
#include <cstring>
#include <algorithm>
#include <numeric>
#include <stack>
#include <functional>
 
using namespace std;
 
#define endl '\n'
#define MOD 1000000007
#define INF 1ll<<30
#define MAX 100010
#define eps 1e-11
#define bit_max 1ll<<32
#define _USE_MATH_DEFINES

long double dp[4000][4000];

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
   // freopen("input.txt","r",stdin);
  //  freopen("output.txt","w",stdout);
    string a;
    cin>>a;
    int ctr = 0;
    for(int i=0;i<a.length();i++)
    {
    	if(a[i]=='0')
    		ctr++;
    }	
    cout<<min(ctr,a.length()-ctr)*2;
}