Problem:
Score : 300 points

Problem Statement

N tiles are arranged in a row from left to right. The initial color of each tile is represented by a string S of length N.

The i-th tile from the left is painted black if the i-th character of S is 0, and painted white if that character is 1.

You want to repaint some of the tiles black or white, so that any two adjacent tiles have different colors.

At least how many tiles need to be repainted to satisfy the condition?

Constraints

1 \leq |S| \leq 10^5

S_i is 0 or 1.

Input

Input is given from Standard Input in the following format:

S

Output

Print the minimum number of tiles that need to be repainted to satisfy the condition.

Sample Input 1

000

Sample Output 1

1

The condition can be satisfied by repainting the middle tile white.

Sample Input 2

10010010

Sample Output 2

3

Sample Input 3

0

Sample Output 3

0

Solution in Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	sc := bufio.NewScanner(os.Stdin)
	buf := make([]byte, 10000)
	sc.Buffer(buf, 100000+1024)

	s := readLine(sc)
	sInts := strings.Split(s, "")

	outputValue := 0
	var tileColorNumber string

	for index, sInt := range sInts {
		if index == 0 {
			tileColorNumber = sInt
			continue
		}

		if tileColorNumber == sInt {
			outputValue++
			if tileColorNumber == "0" {
				tileColorNumber = "1"
			} else {
				tileColorNumber = "0"
			}
		} else {
			tileColorNumber = sInt
		}
	}

	fmt.Println(outputValue)
}

// helper

func readLine(sc *bufio.Scanner) string {
	sc.Scan()
	return strings.TrimSpace(sc.Text())
}

func readLineToInt(sc *bufio.Scanner) int {
	intValue, err := strconv.Atoi(readLine(sc))
	if err != nil {
		panic(err)
	}

	return intValue
}

func explodeString(delimiter string, inputValue string) []string {
	splittedValue := strings.Split(inputValue, delimiter)

	var trimmedValues []string

	for _, value := range splittedValue {
		if value != "" {
			trimmedValues = append(trimmedValues, value)
		}
	}

	return trimmedValues
}

func explodeInt(delimiter string, inputValue string) []int {
	inputStrings := explodeString(" ", inputValue)

	var splittedInts []int

	for _, inputString := range inputStrings {
		var (
			intValue int
			err      error
		)
		intValue, err = strconv.Atoi(inputString)

		if err != nil {
			panic(err)
		}
		splittedInts = append(splittedInts, intValue)
	}

	return splittedInts
}