#include <iostream>
#include <string>

using namespace std;

int main() {
    string str;
    cin >> str;
    int cnt = 0;
    for (size_t i = 1; i < str.size(); ++i) {
        if (str[i - 1] == str[i]) {
            ++cnt;
        }
    }
    cout << (cnt % 2 == 1 ? cnt / 2 + 1 : cnt / 2) << endl;
    return 0;
}