#include "bits/stdc++.h"
using namespace std;
#define int long long
#define endl '\n'
int mod=1e9+7;
int mod2=998244353;
const int INF=1e9;

signed main(){
  string s;
  cin>>s;
  int a=0;
  int b=0;
  for(int i=0;i<s.size();i++){
    if(s[i]=='0')a++;
    else b++;
  }
  cout<<min(a,b)*2<<endl;
}

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