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"
	"os"
	"strconv"
	"strings"
)

var sc = bufio.NewScanner(os.Stdin)

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func nextStr() string {
	sc.Scan()
	s := sc.Text()
	return s
}

func main() {
	sc.Split(bufio.ScanWords)

	N := nextInt()

	var stones string
	for i := 0; i < N; i++ {
		stones += nextStr()
	}

	sharpNum := strings.Count(stones, "#")
	index := strings.Index(stones, "#")
	if index < 0 {
		fmt.Print(0)
		return
	}
	if sharpNum < N/2 {
		dotIndex := strings.Index(stones, "#")
		if dotIndex > N/2 {
			dot := strings.Count(stones, ".")
			fmt.Print(dot)
			return
		}
		sharp := strings.Count(stones, "#")
		fmt.Print(sharp)
		return
	}

	newstones := stones[index:]
	dotIndex := strings.LastIndex(stones, ".")
	if dotIndex > N/2 {
		dot := strings.Count(stones, "#")
		fmt.Print(dot)
		return
	}
	dot := strings.Count(newstones, ".")
	fmt.Print(dot)
	return
}