Problem:
Score : 300 points

Problem Statement

There are N stones arranged in a row. Every stone is painted white or black.
A string S represents the color of the stones. The i-th stone from the left is white if the i-th character of S is ., and the stone is black if the character is #.

Takahashi wants to change the colors of some stones to black or white so that there will be no white stone immediately to the right of a black stone.
Find the minimum number of stones that needs to be recolored.

Constraints

1 \leq N \leq 2\times 10^5

S is a string of length N consisting of . and #.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the minimum number of stones that needs to be recolored.

Sample Input 1

3
#.#

Sample Output 1

1

It is enough to change the color of the first stone to white.

Sample Input 2

5
#.##.

Sample Output 2

2

Sample Input 3

9
.........

Sample Output 3

0

Solution in Go (1.6) (judge verdict: Wrong Answer)

package main

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

var sc = bufio.NewScanner(os.Stdin)
var out = bufio.NewWriter(os.Stdout)

func main() {
	/*/TODO:!!!!!!!テスト用!!!!!!!!!
	sc = bufio.NewScanner(strings.NewReader(`
									`))
	//TODO:!!!!!!!テスト用!!!!!!!!!*/

	buf := make([]byte, 1024*1024)
	sc.Buffer(buf, bufio.MaxScanTokenSize)
	sc.Split(bufio.ScanWords)
	defer out.Flush() // !!!!caution!!!! you must use Fprint(out, ) not Print()
	/* --- code --- */
	//fmt.Fprintln(out, "[DEBUG]", time.Now())

	n := nextInt()
	s := next()

	ans := n
	w := 0
	b := 0
	cw := s[0] == '.'

	for i := 0; i < n; i++ {
		if s[i] == '.' {
			w++
		}
	}
	for i := 0; i < n; i++ {
		if (cw && s[i] == '#') || ((!cw) && s[i] == '.') {
			if cw {
				ans = minInt(ans, b+w)
			}
			cw = !cw
		}

		if s[i] == '#' {
			b++
		} else {
			w--
		}
	}

	ans = minInt(ans, b+w)

	//fmt.Fprintln(out, "[DEBUG]", a)
	fmt.Fprintln(out, ans)
}

//------------------------------------------------------------------------------

// -*-*-*-*-*-*-*-*-
// * I/O utilities *
// -*-*-*-*-*-*-*-*-

func next() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	a, _ := strconv.Atoi(next())
	return a
}

func nextFloat64() float64 {
	a, _ := strconv.ParseFloat(next(), 64)
	return a
}

func nextInts(n int) []int {
	ret := make([]int, n)
	for i := 0; i < n; i++ {
		ret[i] = nextInt()
	}
	return ret
}
func nextFloats(n int) []float64 {
	ret := make([]float64, n)
	for i := 0; i < n; i++ {
		ret[i] = nextFloat64()
	}
	return ret
}
func nextStrings(n int) []string {
	ret := make([]string, n)
	for i := 0; i < n; i++ {
		ret[i] = next()
	}
	return ret
}

func chars(s string) []string {
	ret := make([]string, len([]rune(s)))
	for i, v := range []rune(s) {
		ret[i] = string(v)
	}
	return ret
}

func absInt(x int) int {
	return int(math.Abs(float64(x)))
}
func minInt(x, y int) int {
	if x < y {
		return x
	}
	return y
}
func maxInt(x, y int) int {
	if x > y {
		return x
	}
	return y
}
func log10(x int) float64 {
	return math.Log10(float64(x))
}