#include <bits/stdc++.h>
using namespace std;
int main() {
  string S;
  int cnt_0 = 0, cnt_1 = 0;
  for (int i = 0; i < S.size(); i++) {
    if (S[i] == '0')
      cnt_0++;
    else
      cnt_1++;
  }
  cout << min(cnt_0, cnt_1) * 2 << endl;
  return 0;
}
