#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <array>
#include <map>
#include <stack>
#include <queue>
#include <set>
#include <cmath>

using namespace std;

int numOfZero(string s) {
    int counter = 0;
    for (auto x : s) {
        if (x == '0') {
            counter += 1;
        }
    }
    return counter;
}

int main() {

    string N;
    cin >> N;

    cout << abs(numOfZero("1000000007") - numOfZero(N)) << "\n";
}