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, &s)

	const white, black = '.', '#'
	beforeColor, toBlackCount, toWhiteCount := '.', 0, 0
	for i := 0; i < n; i++ {
		currentColor := int32(s[i])
		if beforeColor == black && currentColor == white {
			toBlackCount++
			currentColor = black
		} else if currentColor == black && i != n - 1 {
			toWhiteCount++
		}
		beforeColor = currentColor
	}

	var result int
	if toBlackCount < toWhiteCount {
		result = toBlackCount
	} else {
		result = toWhiteCount
	}
	fmt.Print(result);
}