#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0;i < (n);i++)
using namespace std;
using ll = long long;
using pii = pair<int,int>;

int main(){
    string s;
    cin >> s;
    int a = 0,b = 0;
    rep(i,s,size()){
        if(s[i] == '1')a++;
        else b++;
    }
    cout << min(a,b)*2 << endl;
}
