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 (
	"fmt"
)

func main() {
	var n int
	var s string
	fmt.Scan(&n)
	fmt.Scan(&s)

	count := 0
	left := 0
	for left < n - 1 {
		if s[left: left + 1] == "#" {
			for left < n - 1 && s[left + 1: left + 2] == "." {
				count++
				left++
			}
		}
		left++
	}

	min := count

	right := n
	count = 0
	for right > 1 {
		if s[right - 1: right] == "." {
			for right > 1 && s[right - 2: right - 1] == "#" {
				count++
				right--
			}
		}
		right--
	}

	if min > count {
		min = count
	}
	fmt.Println(min)
}