#pragma GCC optimize("Ofast")
//#pragma GCC target("avx2")
//#pragma GCC optimize("O3")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

#include "bits/stdc++.h"
using namespace std;

#define _CRT_SECURE_NO_WARINGS
#define INIT ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr)
#define ALL(obj) (obj).begin(),(obj).end()
#define RALL(obj) (obj).rbegin(),(obj).rend()
#define SORT(obj) sort(ALL(obj))
#define RSORT(obj) sort(RALL(obj))
#define REP(i,n) for(int i = 0; i < (n); ++i)
#define COUT_ALL(x) for(auto i=x.begin();i!=--x.end();i++)cout<<*i<<" ";cout<<*--x.end()<<endl;

using ll = long long;

const int INF = 1e9;
const int MOD = 1e9 + 7;
const ll LINF = 1e18;
const double PI = 3.14159265358979323846;

template<class T>bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }

template<typename T>
istream& operator >> (istream& is, vector<T>& vec) {for (T& x : vec) is >> x;return is;}
template<typename T>
ostream& operator << (ostream& os, vector<T>& vec) {
	for (int i = 0; i < vec.size(); i++) { os << vec[i] << (i + 1 == vec.size() ? "" : " "); }
	return os;}

int ctoi(char c) { return (c >= '0' && c <= '9') ? c - '0' : 0; }
void out(bool ans) { cout << (ans ? "Yes" : "No") << "\n"; }

#pragma region F

#pragma endregion

signed main()
{
	INIT; // 必須
	
	string s;
	cin >> s;
	string a = to_string(MOD);
	int x = count(ALL(s), '0');
	int y = count(ALL(a), '0');
	cout << abs(x - y) << "\n";

}