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 Kotlin (1.0.0) (judge verdict: Accepted)

fun main(args: Array<String>) {
	val n = (readLine() ?: return).toInt()
	val s = (readLine() ?: return).toCharArray()
	var white = 0
	for (i in s.indices) if (s[i] == '.') white++
	var min = if (white > s.size) s.size - white else white
	var black = 0
	for (i in s.indices) {
		if (s[i] == '#') black++
		else if (s[i] == '.') {
			white--
			min = Math.min(min, black + white)
		}
	}
	print(min)
}