#include<iostream>
#include<string>
#include<cmath>
using namespace std;
int main()
{
	string s;
	long long n=-1000,count;
	cin>>s;
	for (long long i=0;i<s.length();i++)
	{
		count=0;
		for (long long j=i;j<s.length();j++)
		{
			if (s[j]=='0') count++;
			else count--;
			n=max(n,count);
		}
	}
	cout<<n;
	return 0;
 }