#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9 + 5;
const long long MOD = 1000000007LL;
string abc = "abcdefghijklmnopqrstuvwxyz";
string ABC = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
int main() {
  string s;
  long long one = 0, zero = 0;
  for (long long i = 0; i < (long long)(s.size()); i++) {
    if (s[i] = '0')
      zero++;
    else
      one++;
  }
  cout << 2 * min(one, zero) << endl;
}
