#include <bits/stdc++.h>
#include<vector>
using namespace std;
#define rep(i, n)        for(int i=0; i<(int)(n); ++i)
int main() {
  string a;
  int b,c;
  rep(i,a.size()){
    if(s[i]=='0')b++;
    else c++;
  }
  cout<<(max(b,c)-min(b,c))*2;
}
