#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int main() {
	string st;
	cin >> st;
	int num_0 = 0;
	int num_1 = 0;
	char ch;
	for (int i = 0; i < st.length; ++i) {
		ch = st[i];
		if (ch == '0') num_0++;
		if (ch == '1') num_1++;
	}
	cout << min(num_0, num_1) << endl;
	return 0;
}
