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"
	"io"
	"os"
	"strings"
)

func solve(w io.Writer, r io.Reader) {
	var N int
	var S string
	fmt.Fscan(r, &N, &S)
	S = strings.TrimLeft(S, ".")
	S = strings.TrimRight(S, "#")

	var black, white int
	var stones []int
	for i := 0; i < len(S); i++ {
		if S[i] == '#' {
			black++
			if white > 0 {
				stones = append(stones, white)
				white = 0
			}
		} else {
			white++
			if black > 0 {
				stones = append(stones, black)
				black = 0
			}
		}
	}
	if white > 0 {
		stones = append(stones, white)
	}

	ans := 0
	for i := 0; i < len(stones); i += 2 {
		c := 0
		for j := i + 1; j < len(stones); j += 2 {
			c += stones[j]
			if stones[i] < c {
				break
			}
		}
		if stones[i] < c {
			ans += stones[i]
		} else {
			ans += c
			break
		}
	}
	fmt.Fprintln(w, ans)
}

func main() {
	solve(os.Stdout, os.Stdin)
}