#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  cin >> s;
  int sum = 0;
  for (int i = 0; i < s.length(); i++) {
    if (s[i] == '0' && s[i + 1] == '1' || s[i] == '1' && s[i + 1] == '0') {
      for (int j = i; j < s.length(); j++) {
        s[j] = s[j + 2];
      }
      sum += 4;
    }
  }
  cout << sum << endl;
  return 0;
}
