#include <bits/stdc++.h>
#include <cstdlib>
using namespace std;

int main(){
    string l; cin >> l;
    const string S =l;
    int N = S.size();

    int s[100010]; for (int i = 0; i < N; i++) s[i] = atoi(S.at(i));

    int sum_0 = 0, sum_1 = 0;
    for (int i = 0; i < N; i++) {
        if (s[i] = 0) sum_0 ++;
        else sum_1 ++;
    }

    cout << 2*(min(sum_0, sum_1)) << endl;
}