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"
)

func readLine(sc *bufio.Scanner) string {
	sc.Scan()
	return sc.Text()
}

func min(a, b int64) int64 {
	if a <= b {
		return a
	}
	return b
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	buf := make([]byte, 10000)
	sc.Buffer(buf, 10000000)

	readLine(sc)
	s := readLine(sc)

	wCnt, bCnt, wkBCnt := int64(0), int64(0), int64(0)
	for _, o := range s {
		if o == '.' {
			wCnt++
			bCnt += wkBCnt
			wkBCnt = 0
		} else {
			wkBCnt++
		}
	}

	fmt.Println(min(wCnt, bCnt))
}