#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define MAX 200000

int main(){
	char *input;
	int i;
	input = (char*) malloc(MAX *sizeof(char));

	scanf("%s", input);
	
	int count = 0;
	for(i=0;i<strlen(input)-2; i+=2){
		if(input[i]!=input[i+2]&&input[i+1]!=input[i+3]){
			count++;
		}
	}

	if (count%2==1){
		printf("%d", (count/2)+1);
	} else {
		printf("%d",count/2);
	}

	return 0;
}