#define REP(i, n) for (int i = 0; i < (n); ++i)

#include <algorithm>
#include <iostream>
#include <vector>

using namespace std;
signed main() {
  ios::sync_with_stdio(false);
  string s;
  cin >> s;
  long long sum = 0;
  REP(i, s.length) {
      if(s[i] == '0') sum++;
  }
  cout << min({sum, (long long)s.length - sum}) * 2 << endl;
  return 0;
}
