#include <bits/stdc++.h>
using namespace std;
struct Fast {
  Fast() {
    std::cin.tie(0);
    ios::sync_with_stdio(false);
  }
} fast;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using pii = pair<int, int>;
using vll = vector<long long>;
using pll = pair<ll, ll>;
int main() {
  string second;
  int num = 0;
  int N = second.size();
  for (int i = 0; i < (int)(N); i++) {
    if (second[i] == '0') num++;
  }
  cout << 2 * min(num, N - num) << endl;
}
