#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
    string s;
    cin>>s;
    int z=o=0;
    for (auto c:s) {
        if (c=='0')
            z++;
        else o++;
    }
    cout<<min(z,o)*2<<endl;
    return 0;
}