#include <bits/stdc++.h>
int main() {
  std::string S;
  long long int cnt = 0;
  for (long long int i = 0; i < S.length(); ++i)
    if (S[i] == '0') ++cnt;
  std::cout << std::min<long long int>(cnt, S.length() - cnt) * 2 << std::endl;
}
