#include <iostream>
#include <vector>
#include <string>
#include <math.h>

int main()
{
	std::string input;
	
	std::cin >> input;
	unsigned int output = 0;
	
	char prev = input[0];
	for(unsigned int i = 1; i < input.size() - 1; i++)
	{
		if(prev == input[i])
		{
			output++;
		}
		prev = input[i];
	}
	
	output = ceil((float)output / 2);
	
	std::cout << output << std::endl;
	
	
	return 0;
};