#include <bits/stdc++.h>
int main() {
  int zero = 0;
  int one = 0;
  char c;
  while ((c = getc(stdin)) != EOF) {
    if (c == '0') {
      zero++;
      continue;
    }
    one++;
  }
  printf("%d\n", std::min(zero, one) * 2);
}
