#include <bits/stdc++.h>
using namespace std;
int main() {
  vector<char> a;
  string b;
  int zero = 0;
  int one = 0;
  cin >> b;
  if (a.size() == 1) {
    cout << "ee" << endl;
    cout << 0 << endl;
    return 1;
  }
  string tmp;
  for (int i = 0; i < b.size(); i++) {
    tmp = b[i];
    if (tmp == "0")
      zero++;
    else
      one++;
  }
  if (zero < one)
    cout << one * 2 << endl;
  else
    cout << zero * 2 << endl;
}
