#include <iostream>
#include<bits/stdc++.h>

using namespace std;
int main() {
    string journals;
    int changesCount = 0;
    int startR = 0;
    int endR = 0;
    char previousSign = '1';
    cin >> journals;
    for (int i = 0; i < journals.size(); i++) {
        if (journals[i] == previousSign) {
            previousSign = journals[i];
            if (i == journals.size()-1) {
                changesCount++;
                break;
            }
            for (int j = i+1; j < journals.size(); j++) {
                if(journals[j] == previousSign || journals.size() == j+1) {
                    changesCount++;
                    i = j;
                    previousSign = journals[j];
                    break;
                }
            }
            } else {
            previousSign = journals[i];
        }
    }
    cout<<changesCount<<endl;
    return 0;
}