// C++ includes used for precompiling -*- C++ -*-

// Copyright (C) 2003-2013 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file stdc++.h
 *  This is an implementation file for a precompiled header.
 */

// 17.4.1.2 Headers

// C
#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

#if __cplusplus >= 201103L
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
// #include <cstdalign>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
#endif

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#if __cplusplus >= 201103L
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#endif

using namespace std;

int main()
{

  string s;
  cin >> s;
  long long int n0=0,n1=0;

  // s = "01010100";
  // s.erase(1, 3);
  // cout << s << endl;

  // while (1)
  // {
  for (int i = 0; i < s.length(); i++)
  {
    if(s[i]=='0'){
      n0++;
    }
    else if(s[i]=='1'){
      n1++;
    }
  }
  //   if (count == counta)
  //   {
  //     break;
  //   }
  //   counta = count;
  // }
  cout << 2 *min(n0,n1)  << endl;

  return 0;
}
// int main()
// {

//   int A, B, K;
//   int i = 0;

//   int count = 0;
//   cin >> A >> B >> K;

//   if (A > B)
//   {
//     i = B;
//   }
//   else
//   {
//     i = A;
//   }

//   while (i >= 1)
//   {

//     if (A % i == 0 && B % i == 0)
//     {
//       count++;
//     }
//     if (count == K)
//     {
//       break;
//     }
//     i--;
//   }

//   cout << i << endl;

//   return 0;
// }

// int main()
// {

//   int A, B, C;

//   cin >> A >> B >> C;

//   if (A > B)
//   {
//     cout << 0 << endl;
//   }
//   else
//   {
//     if (B / A >= C)
//     {
//       cout << C << endl;
//     }
//     else
//     {
//       cout << B/A << endl;
//     }
//   }

//   return 0;
// }


Measured memory_bytes: 512