
int solve() {
    string s;
    cin >> s;
    ll a, b;

    for(string::iterator it = s.begin(); it != s.end(); ++it) {
        if (*it == '1') {
            ++a;
        } else {
            ++b;
        }
    }
    int m = min(a, b) * 2;
    return m;
}

int main(void){
    cin.tie(0);
    ios::sync_with_stdio(false);

    cout << solve();
    return 0;
}