Problem:
Score : 200 points

Problem Statement

Takahashi lives in another world. There are slimes (creatures) of 10000 colors in this world. Let us call these colors Color 1, 2, ..., 10000.

Takahashi has N slimes, and they are standing in a row from left to right. The color of the i-th slime from the left is a_i.
If two slimes of the same color are adjacent, they will start to combine themselves. Because Takahashi likes smaller slimes, he has decided to change the colors of some of the slimes with his magic.

Takahashi can change the color of one slime to any of the 10000 colors by one spell.
How many spells are required so that no slimes will start to combine themselves?

Constraints

2 \leq N \leq 100

1 \leq a_i \leq N

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
a_1 a_2 ... a_N

Output

Print the minimum number of spells required.

Sample Input 1

5
1 1 2 2 2

Sample Output 1

2

For example, if we change the color of the second slime from the left to 4, and the color of the fourth slime to 5, the colors of the slimes will be 1, 4, 2, 5, 2, which satisfy the condition.

Sample Input 2

3
1 2 1

Sample Output 2

0

Although the colors of the first and third slimes are the same, they are not adjacent, so no spell is required.

Sample Input 3

5
1 1 1 1 1

Sample Output 3

2

For example, if we change the colors of the second and fourth slimes from the left to 2, the colors of the slimes will be 1, 2, 1, 2, 1, which satisfy the condition.

Sample Input 4

14
1 2 2 3 3 3 4 4 4 4 1 2 3 4

Sample Output 4

4

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

package main

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"math"
	"os"
	"strconv"
	"strings"
)

/*********** I/O ***********/

var (
	// ReadString returns a WORD string.
	ReadString func() string
	stdout     *bufio.Writer
)

func init() {
	ReadString = newReadString(os.Stdin)
	stdout = bufio.NewWriter(os.Stdout)
}

func newReadString(ior io.Reader) func() string {
	r := bufio.NewScanner(ior)
	r.Buffer(make([]byte, 1024), int(1e+11))
	// Split sets the split function for the Scanner. The default split function is ScanLines.
	// Split panics if it is called after scanning has started.
	r.Split(bufio.ScanWords)

	return func() string {
		if !r.Scan() {
			panic("Scan failed")
		}
		return r.Text()
	}
}

// ReadInt returns an integer.
func ReadInt() int {
	return int(readInt64())
}

func readInt64() int64 {
	i, err := strconv.ParseInt(ReadString(), 0, 64)
	if err != nil {
		panic(err.Error())
	}
	return i
}

// ReadIntSlice returns an integer slice that has n integers.
func ReadIntSlice(n int) []int {
	b := make([]int, n)
	for i := 0; i < n; i++ {
		b[i] = ReadInt()
	}
	return b
}

// ReadRuneSlice returns a rune slice.
func ReadRuneSlice() []rune {
	return []rune(ReadString())
}

/*********** DP sub-functions ***********/

// ChMin accepts a pointer of integer and a target value.
// If target value is SMALLER than the first argument,
//	then the first argument will be updated by the second argument.
func ChMin(updatedValue *int, target int) bool {
	if *updatedValue > target {
		*updatedValue = target
		return true
	}
	return false
}

// ChMax accepts a pointer of integer and a target value.
// If target value is LARGER than the first argument,
//	then the first argument will be updated by the second argument.
func ChMax(updatedValue *int, target int) bool {
	if *updatedValue < target {
		*updatedValue = target
		return true
	}
	return false
}

// GetNthBit returns nth bit value of an argument.
// n starts from 0.
func GetNthBit(num, nth int) int {
	return num >> uint(nth) & 1
}

/*********** Arithmetic ***********/

// Max returns the max integer among input set.
// This function needs at least 1 argument (no argument causes panic).
func Max(integers ...int) int {
	m := integers[0]
	for i, integer := range integers {
		if i == 0 {
			continue
		}
		if m < integer {
			m = integer
		}
	}
	return m
}

// Min returns the min integer among input set.
// This function needs at least 1 argument (no argument causes panic).
func Min(integers ...int) int {
	m := integers[0]
	for i, integer := range integers {
		if i == 0 {
			continue
		}
		if m > integer {
			m = integer
		}
	}
	return m
}

// CeilInt returns the minimum integer larger than or equal to float(a/b).
func CeilInt(a, b int) int {
	res := a / b
	if a%b > 0 {
		res++
	}
	return res
}

// FloorInt returns the maximum integer smaller than or equal to float(a/b)
func FloorInt(a, b int) int {
	res := a / b
	return res
}

// PowInt is integer version of math.Pow
// PowInt calculate a power by Binary Power (二分累乗法(O(log e))).
func PowInt(a, e int) int {
	if a < 0 || e < 0 {
		panic(errors.New("[argument error]: PowInt does not accept negative integers"))
	}

	if e == 0 {
		return 1
	}

	if e%2 == 0 {
		halfE := e / 2
		half := PowInt(a, halfE)
		return half * half
	}

	return a * PowInt(a, e-1)
}

// AbsInt is integer version of math.Abs
func AbsInt(a int) int {
	if a < 0 {
		return -a
	}
	return a
}

// Gcd returns the Greatest Common Divisor of two natural numbers.
// Gcd only accepts two natural numbers (a, b >= 1).
// 0 or negative number causes panic.
// Gcd uses the Euclidean Algorithm.
func Gcd(a, b int) int {
	if a <= 0 || b <= 0 {
		panic(errors.New("[argument error]: Gcd only accepts two NATURAL numbers"))
	}
	if a < b {
		a, b = b, a
	}

	// Euclidean Algorithm
	for b > 0 {
		div := a % b
		a, b = b, div
	}

	return a
}

// Lcm returns the Least Common Multiple of two natural numbers.
// Lcd only accepts two natural numbers (a, b >= 1).
// 0 or negative number causes panic.
// Lcd uses the Euclidean Algorithm indirectly.
func Lcm(a, b int) int {
	if a <= 0 || b <= 0 {
		panic(errors.New("[argument error]: Gcd only accepts two NATURAL numbers"))
	}

	// a = a'*gcd, b = b'*gcd, a*b = a'*b'*gcd^2
	// a' and b' are relatively prime numbers
	// gcd consists of prime numbers, that are included in a and b
	gcd := Gcd(a, b)

	// not (a * b / gcd), because of reducing a probability of overflow
	return (a / gcd) * b
}

/*********** Utilities ***********/

// DeleteElement returns a *NEW* slice, that have the same and minimum length and capacity.
// DeleteElement makes a new slice by using easy slice literal.
func DeleteElement(s []int, i int) []int {
	if i < 0 || len(s) <= i {
		panic(errors.New("[index error]"))
	}
	// appendのみの実装
	n := make([]int, 0, len(s)-1)
	n = append(n, s[:i]...)
	n = append(n, s[i+1:]...)
	return n
}

// Concat returns a *NEW* slice, that have the same and minimum length and capacity.
func Concat(s, t []rune) []rune {
	n := make([]rune, 0, len(s)+len(t))
	n = append(n, s...)
	n = append(n, t...)
	return n
}

// UpperRune is rune version of `strings.ToUpper()`.
func UpperRune(r rune) rune {
	str := strings.ToUpper(string(r))
	return []rune(str)[0]
}

// LowerRune is rune version of `strings.ToLower()`.
func LowerRune(r rune) rune {
	str := strings.ToLower(string(r))
	return []rune(str)[0]
}

// ToggleRune returns a upper case if an input is a lower case, v.v.
func ToggleRune(r rune) rune {
	var str string
	if 'a' <= r && r <= 'z' {
		str = strings.ToUpper(string(r))
	} else if 'A' <= r && r <= 'Z' {
		str = strings.ToLower(string(r))
	} else {
		str = string(r)
	}
	return []rune(str)[0]
}

// ToggleString iteratively calls ToggleRune, and returns the toggled string.
func ToggleString(s string) string {
	inputRunes := []rune(s)
	outputRunes := make([]rune, 0, len(inputRunes))
	for _, r := range inputRunes {
		outputRunes = append(outputRunes, ToggleRune(r))
	}
	return string(outputRunes)
}

// Strtoi is a wrapper of `strconv.Atoi()`.
// If `strconv.Atoi()` returns an error, Strtoi calls panic.
func Strtoi(s string) int {
	if i, err := strconv.Atoi(s); err != nil {
		panic(errors.New("[argument error]: Strtoi only accepts integer string"))
	} else {
		return i
	}
}

/*********** Permutation ***********/

// memo: 10! == 3628800 > 3M
func CalcFactorialPatterns(elements []rune) [][]rune {
	copiedResidual := make([]rune, len(elements))
	copy(copiedResidual, elements)
	return factorialRecursion([]rune{}, copiedResidual)
}
func factorialRecursion(interim, residual []rune) [][]rune {
	if len(residual) == 0 {
		return [][]rune{interim}
	}

	res := [][]rune{}
	for idx, elem := range residual {
		copiedInterim := make([]rune, len(interim))
		copy(copiedInterim, interim)
		copiedInterim = append(copiedInterim, elem)
		copiedResidual := genDeletedSlice(idx, residual)
		res = append(res, factorialRecursion(copiedInterim, copiedResidual)...)
	}

	return res
}
func genDeletedSlice(delId int, S []rune) []rune {
	res := []rune{}
	res = append(res, S[:delId]...)
	res = append(res, S[delId+1:]...)
	return res
}

// memo: 3**10 == 59049
func CalcDuplicatePatterns(elements []rune, digit int) [][]rune {
	return duplicateRecursion([]rune{}, elements, digit)
}
func duplicateRecursion(interim, elements []rune, digit int) [][]rune {
	if len(interim) == digit {
		return [][]rune{interim}
	}

	res := [][]rune{}
	for i := 0; i < len(elements); i++ {
		copiedInterim := make([]rune, len(interim))
		copy(copiedInterim, interim)
		copiedInterim = append(copiedInterim, elements[i])
		res = append(res, duplicateRecursion(copiedInterim, elements, digit)...)
	}

	return res
}

// usage
//tmp := CalcFactorialPatterns([]rune{'a', 'b', 'c'})
//expected := []string{"abc", "acb", "bac", "bca", "cab", "cba"}
//tmp := CalcDuplicatePatterns([]rune{'a', 'b', 'c'}, 3)
//expected := []string{"aaa", "aab", "aac", "aba", "abb", "abc", ...}

/*********** Binary Search ***********/

func GeneralLowerBound(s []int, key int) int {
	isOK := func(index, key int) bool {
		if s[index] >= key {
			return true
		}
		return false
	}

	ng, ok := -1, len(s)
	for int(math.Abs(float64(ok-ng))) > 1 {
		mid := (ok + ng) / 2
		if isOK(mid, key) {
			ok = mid
		} else {
			ng = mid
		}
	}

	return ok
}

func GeneralUpperBound(s []int, key int) int {
	isOK := func(index, key int) bool {
		if s[index] > key {
			return true
		}
		return false
	}

	ng, ok := -1, len(s)
	for int(math.Abs(float64(ok-ng))) > 1 {
		mid := (ok + ng) / 2
		if isOK(mid, key) {
			ok = mid
		} else {
			ng = mid
		}
	}

	return ok
}

// usage
//test := []int{1, 2, 2, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 5, 10, 10, 10, 20, 20, 20, 30, 30, 30}
//assert.Equal(t, 5, GeneralUpperBound(test, 5)-GeneralLowerBound(test, 5))
//assert.Equal(t, 0, GeneralUpperBound(test, 15)-GeneralLowerBound(test, 15))

/*********** Union Find ***********/

func InitParents(parents []int, maxNodeId int) {
	for i := 0; i <= maxNodeId; i++ {
		parents[i] = i
	}
}

func unite(x, y int, parents []int) {
	xp, yp := root(x, parents), root(y, parents)
	if xp == yp {
		return
	}

	parents[xp] = yp
}

func same(x, y int, parents []int) bool {
	return root(x, parents) == root(y, parents)
}

func root(x int, parents []int) int {
	if parents[x] == x {
		return x
	}

	parents[x] = root(parents[x], parents)
	return parents[x]
}

/*********** Factorization, Prime Number ***********/

// TrialDivision returns the result of prime factorization of integer N.
// Complicity: O(n)
func TrialDivision(n int) map[int]int {
	if n <= 1 {
		panic(errors.New("[argument error]: TrialDivision only accepts a NATURAL number"))
	}

	p := map[int]int{}
	for i := 2; i*i <= n; i++ {
		exp := 0
		for n%i == 0 {
			exp++
			n /= i
		}

		if exp == 0 {
			continue
		}
		p[i] = exp
	}
	if n > 1 {
		p[n] = 1
	}

	return p
}

// IsPrime judges whether an argument integer is a prime number or not.
func IsPrime(n int) bool {
	if n == 1 {
		return false
	}

	for i := 2; i*i <= n; i++ {
		if n%i == 0 {
			return false
		}
	}

	return true
}

/*********** Inverse Element ***********/

// CalcNegativeMod can calculate a right residual whether value is positive or negative.
func CalcNegativeMod(val, m int) int {
	res := val % m
	if res < 0 {
		res += m
	}
	return res
}

func modpow(a, e, m int) int {
	if e == 0 {
		return 1
	}

	if e%2 == 0 {
		halfE := e / 2
		half := modpow(a, halfE, m)
		return half * half % m
	}

	return a * modpow(a, e-1, m) % m
}

// CalcModInv returns $a^{-1} mod m$ by Fermat's little theorem.
// O(1), but C is nearly equal to 30 (when m is 1000000000+7).
func CalcModInv(a, m int) int {
	return modpow(a, m-2, m)
}

/********** heap package (Integer Priority Queue) **********/

type IntHeap []int

func (h IntHeap) Len() int           { return len(h) }
func (h IntHeap) Less(i, j int) bool { return h[i] < h[j] }
func (h IntHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
func (h *IntHeap) Push(x interface{}) {
	*h = append(*h, x.(int))
}
func (h *IntHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

// h := &IntHeap{3, 6, 1, 2}
// heap.Init(h)
// heap.Push(h, followers[i])
// poppedD := heap.Pop(h).(int)

/********** sort package (snippets) **********/
//sort.Sort(sort.IntSlice(s))
//sort.Sort(sort.Reverse(sort.IntSlice(s)))
//sort.Sort(sort.Float64Slice(s))
//sort.Sort(sort.StringSlice(s))

// struct sort
type Mono struct {
	key, value int
}
type MonoList []*Mono

func (ml MonoList) Len() int {
	return len(ml)
}
func (ml MonoList) Swap(i, j int) {
	ml[i], ml[j] = ml[j], ml[i]
}
func (ml MonoList) Less(i, j int) bool {
	return ml[i].value < ml[j].value
}

// Example(ABC111::C)
//oddCountList, evenCountList := make(MonoList, 1e5+1), make(MonoList, 1e5+1)
//for i := 0; i <= 1e5; i++ {
//	oddCountList[i] = &Mono{key: i, value: oddMemo[i]}
//	evenCountList[i] = &Mono{key: i, value: evenMemo[i]}
//}
//sort.Sort(sort.Reverse(oddCountList))		// DESC sort
//sort.Sort(sort.Reverse(evenCountList))	// DESC sort

/********** copy function (snippets) **********/
//a = []int{0, 1, 2}
//b = make([]int, len(a))
//copy(b, a)

/********** I/O usage **********/

//str := ReadString()
//i := ReadInt()
//X := ReadIntSlice(n)
//S := ReadRuneSlice()

/********** String Split **********/

//strs := strings.Split(string(runeSlice), "+")

/*******************************************************************/

const MOD = 1000000000 + 7
const ALPHABET_NUM = 26

var n int
var A []int

func main() {
	n = ReadInt()
	A = ReadIntSlice(n)

	ans := 0
	for i := 1; i < n; i++ {
		if A[i-1] == A[i] {
			ans++
			A[i] = -1
		}
	}
	fmt.Println(ans)
}